Greyhound Computer Corporation brought this action against International Business Machines Corporation alleging IBM had monopolized or attempted to monopolize various markets- in the electronic data processing industry in violation of section 2 of the Sherman Act, 15 U.S.C. § 2. Greyhound also charged IBM with breaching contracts to provide certain services in conjunction with the sale of computer equipment. After presentation of Greyhound’s ease the district court granted IBM’s motion for a directed verdict. This appeal followed.
We affirm the directed verdict on the contract issue, but reverse and remand for trial of the monopolization and attempt to monopolize claims.
I. Factual Background and Standard of Review
The computer industry, which is little more than 25 years old, has witnessed the introduction of three (and possibly four) “generations” of equipment, each generation representing a major technological advance. The first computers, introduced in 1952, were built with vacuum tubes. The second generation, introduced in 1958, utilized transistor technology. In 1964 IBM introduced the third generation with the System 360 family of computers, employing integrated circuits and other advances. In 1970 IBM announced an improved third (or possibly fourth) generation, the System 370 line. Because the electronic components of second and third generation equipment are virtually indestructible, the life of this equipment is a function of price and technological obsolescence rather than wear from usage.
*492A computer system consists of a central processing unit (or “mainframe”) and peripheral equipment. Peripheral equipment includes means for storing information such as disk and tape drives, and input and output devices such as printers and terminals. Programmed instructions, or software, must be designed to enable the equipment to perform particular functions. Computer systems vary greatly in size and capacity to perform specified tasks.
IBM manufactures entire computer systems, including mainframes and peripherals. It also provides software and support services to its customers. Like other manufacturers, IBM both leases and sells its computers.
Greyhound is a leasing company; it does not manufacture computers. It buys computers from others and leases them in competition with computer manufacturers and other leasing companies.1
Greyhound is both a customer and competitor of IBM. Greyhound’s antitrust claim is that IBM restricted sales of its computer equipment in order to monopolize the leasing market in which Greyhound competes. Greyhound’s contract claim is that IBM breached an obligation to provide services to Greyhound’s lessees.
The district court granted the motion for a directed verdict on the antitrust claim because (1) the evidence was insufficient to establish a relevant market and IBM’s share of the market; (2) the evidence was insufficient to establish IBM’s control of a market; (3) the share of any market IBM holds “has been achieved as a result of superior skill, foresight, and industry”; (4) IBM’s activity of which Greyhound complains was a competitive response to economic factors over which IBM had no control; and (5) Greyhound’s damages were “purely speculative.” The court directed the verdict on the contract claim because the evidence was insufficient and because the claim was barred by the parol evidence rule, the statute of frauds, and local rules of court.
The standard on review of a directed verdict favors Greyhound. We are “bound to view the evidence in the light most favorable to [Greyhound] and to give it the benefit of all inferences which the evidence fairly supports, even though contrary inferences might reasonably be drawn.” Continental Ore Co. v. Union Carbide, 370 U.S. 690, 696, 82 S.Ct. 1404, 1409, 8 L.Ed.2d 777 (1962).2
II. Monopolization
“The offense of monopoly under § 2 of the Sherman Act has two elements: (1) the possession of monopoly power in the relevant market and (2) the willful acquisition or maintenance of that power as distinguished from growth or development as a consequence of a superior product, business acumen, or historic accident.” United States v. Grinnell Corp., 384 U.S. 563, 570-71, 86 S.Ct. 1698, 1704, 16 L.Ed.2d 778 (1966).3
*493A. The Relevant Market
Greyhound’s major contention is that IBM has monopolized or attempted to monopolize a submarket for leasing general purpose digital computers for commercial application. Greyhound also contends that IBM has monopolized or attempted to monopolize a separate submarket for IBM’s own product line.
The question is whether Greyhound offered evidence from which the jury could have reasonably concluded that the sub-markets which Greyhound defined were sufficiently distinct in commercial reality to permit a company that dominated these submarkets to exclude competition and control prices. This depends upon whether efforts to exclude competition or control prices in the submarkets in question would be negated by a shift of buyers to other portions of the market.4
IBM does not challenge the adequacy of Greyhound’s evidence to establish a market limited to general purpose digital computers for commercial applications. It does argue, however, that the evidence will not support a finding that leasing constitutes a separate submarket. IBM also contends that the record does not establish a sub-market defined exclusively in terms of IBM’s product line.
From the record the jury could have concluded that the market for general purpose computers for commercial applications was distinguishable economically from the market for “dedicated application” computers or other general purpose systems, including minicomputers, process control computers, and large scientific computers.5 Greyhound offered evidence that other computers are not reasonably interchangeable with general purpose commercial systems, and that no significant substitution in fact takes place.6 Other evidence indicated that computer systems manufacturers tend to specialize in but one of these types of computers, that the industry and its customers recognized these categories of computers, and that the various categories have distinct prices and distinct sets of competitors employing different marketing techniques. See Brown Shoe Co. v. United *494States, 370 U.S. 294, 325, 82 S.Ct. 1502, 8 L.Ed.2d 510 (1962).7 This evidence was sufficient to support a jury conclusion that the market for general purpose computer systems for commercial applications constitutes a relevant market for antitrust purposes.
It is a closer question whether the evidence would permit a jury finding that leasing general purpose computers for commercial applications constituted a submarket economically distinct from others in which such computers are made available to users. We conclude, however, that such a finding would have been justified.
No rule of law or economic principle bars application of section 2 of the Sherman Act to one of several alternative means of distributing a product. The statute prohibits monopolization of “any part” of interstate or foreign commerce. Accordingly, the Sherman Act and other antitrust statutes have been applied to protect competition in one of alternate channels of distribution.8
The record indicates that data processing services are distributed to users by: (1) sale of computer systems, (2) lease of computer systems, (3) time-sharing,9 or (4) contracting with service bureaus.10 The latter two are the most clearly discrete. There was ample evidence that service bureaus and time-sharing arrangements do not provide an acceptable alternative to those who might buy or lease computer systems. Greyhound offered testimony that time-sharing and service bureaus are addressed to needs different from those served by an installed computer,11 that purchasers and lessees of computers do not consider service bureau and time-sharing arrangements an acceptable substitute, and that leasing companies do not consider suppliers of these services to be their competitors.
The evidence is not so clear that leasing general purpose computers constitutes a market distinct from selling. Considering the weighty presumption in favor of a jury determination, however, we conclude the evidence was sufficient.
Leases and sales serve different customer needs. Greyhound offered testimony that general purpose commercial computers are purchased by banks, insurance companies, and other businesses with predictable long-term data processing needs and the capacity to undertake long-term financial commitments. Computers are leased by customers that have variable business requirements and a need to keep abreast of advancing technology. A single company with a variety of problems may purchase a computer to perform one task and lease a computer to *495perform another.12 Because lessees retain the option to cancel (albeit at some penalty), even the long-term lessee has a degree of flexibility unavailable to the purchaser. IBM’s senior vice president testified that, at least with some models, the decision to purchase or lease may not be affected by price changes. On this record a jury could infer that the need for flexibility governed the choice between a lease and purchase, and that there was substantial customer resistance to shifting from one to the other.13
The computer industry, as well as its customers, recognized the distinction between the business of selling and the business of leasing. Leasing companies, of course, engaged only in the latter. Moreover, leasing requires a commitment of capital for a substantially greater period of time than selling.
IBM argues that both leasing and buying are merely methods of financing the use of computer systems. However, the Sherman Act cannot be avoided by classifying the commercial activity involved as financing. A difference in services offered by financial institutions may provide the basis for recognition of distinct submarkets for antitrust purposes.14
We conclude that, the evidence was sufficient, though by no great margin, to permit the jury to find that the differences between leasing and selling general purpose computers were of sufficient significance to justify treatment of the two forms of distribution as distinct submarkets for competitive purposes.
In light of this conclusion we need not decide whether IBM’s product line constitutes a separate submarket for antitrust purposes.15 Greyhound offered evidence that although other manufacturers compete with IBM for initial installation, the cost of changing to another manufacturer’s system once a system is installed may be prohibitive.16 Greyhound asserts that by offering a complete product line of general purpose commercial systems, IBM is able to “lock *496in” users who select IBM equipment initially, and limit competition to leasing companies carrying IBM systems. We intimate no view on whether such evidence establishes an economically distinct submarket. Compare Bushie v. Stenocord Corp., 460 F.2d 116, 120-21 (9th Cir. 1972); Industrial Building Materials, Inc. v. Interchemical Corp., 437 F.2d 1336, 1344 (9th Cir. 1970).
B. Possession of Monopoly Power
There was evidence from which the jury could reasonably infer that IBM possessed monopoly power in the leasing of general purpose commercial computers.
“Monopoly power is the power to control prices or exclude competition.” United States v. E. I. duPont de Nemours & Co., 351 U.S. 377, 391, 76 S.Ct. 994, 1005, 100 L.Ed. 1264 (1956). Accord, United States v. Grinnell Corp., supra, 384 U.S. at 571, 86 S.Ct. 1698. “[S]ize is of course an earmark of monopoly power,” United States v. Griffith, 334 U.S. 100, 107 n. 10, 68 S.Ct. 941, 946, 92 L.Ed. 1236 (1948), and “[t]he existence of such power ordinarily may be inferred from the predominant share of the market.” United States v. Grinnell Corp., supra, 384 U.S. at 571, 86 S.Ct. at 1704. The evidence in this record permitted a calculation17 of IBM’s share of revenues from leasing of general purpose computers at 82.5 percent in 1964, 75.1 percent in 1967, and 64.68 percent in 1970.18 The portion of *497the market not controlled by IBM was dispersed among many other companies, none accounting for more than 4 percent of total lease revenues. Eight firms manufactured over 95 percent of the general purpose computers,19 and IBM’s share of the general purpose commercial lease revenues of this group of the strongest competitors in the relevant market was 83.7 percent in 1964, 78.9 percent in 1967, and 77.7 percent in 1970. The revenue of each of the other seven was relatively insubstantial.
Evidence other than IBM’s predominant share of the market supported an inference of market dominance. About 80 percent in dollar value of the installed base of general purpose systems is IBM equipment. IBM derived substantial market leverage from the fact that the vast majority of installed computer systems are IBM built. There was evidence that because of the high changeover costs faced by customers who wish to change equipment manufacturers, the rental demand for IBM systems among current IBM users was inflexible. IBM’s senior vice president testified that rental prices of some models could be increased without proportionate decreases in demand. Other evidence indicating IBM’s ability to manage its prices with little regard to competition included testimony that IBM based its prices on a 30 percent profit objective, that it never set a price simply to meet competition, and that its prices were 5 to 15 percent above those of the best of its competition.
IBM responds that other evidence in the record indicates IBM did not possess monopoly power. None of this evidence compelled a ruling in IBM’s favor as a matter of law. IBM argues, for example, that the “youth, change and growth” of the computer industry are inconsistent with a finding of monopoly power. These characteristics, however, do not immunize an industry from monopolization, and, in any event, nothing in the record suggests that IBM’s own power was transient. IBM also argues that entry into the industry is easy, and that IBM’s competitors are strong and independent. But the record suggests new entrants avoided direct confrontation with IBM and occupied interstices in the market. Two substantial competitors who met IBM directly in the marketplace (RCA and General Electric) bowed out after sustaining heavy losses. The record also suggests that IBM’s dominant installed base and high changeover costs have created a barrier to entry at the manufacturing level so substantial that only leasing companies will be able to initiate competition with IBM for this large group of users.20
IBM also contends that price reduction and product improvement are characteristics of the industry and are inconsistent with the existence of monopoly power. But rapid technological progress may provide a climate favorable to increased concentration of market power rather than the opposite.21 Moreover, a decline in prices does not necessarily imply an absence of monopoly power; a fair profit might have been made at even lower cost to users. See United States v. Aluminum Company of America, 148 F.2d 416, 427 (2d Cir. 1945). Finally, IBM asserts that because of competition from other companies its revenue fell $220 million from 1968 to 1969 and $150 million from 1969 to 1970. But IBM offered quite a different explanation to its shareholders, informing them that the decline was the result of cyclical purchases and an adverse economy.
*498C. Willful Acquisition or Maintenance of Monopoly Power
The gravamen of Greyhound’s complaint is that IBM undertook to advance IBM’s own leasing operations at the expense of leasing companies by making the purchase of computer equipment for lease economically unattractive.22
There was ample evidence that IBM officials became concerned that the balance between sales and rental had turned too heavily toward sales, and deliberately set about to reverse the trend. Greyhound asserts that in pursuit of this goal IBM adopted certain practices that reflect “the willful acquisition or maintenance of [monopoly] power as distinguished from growth or development as a consequence of a superior product, business acumen, or historic accident.” United States v. Grinnell Corp., supra, 384 U.S. at 570-71, 86 S.Ct. at 1704.
These practices were (1) inaugurating the “fixed term plan,” (2) eliminating the technological discount, (3) increasing the “multiplier” (a ratio describing the relationship of IBM purchase price to IBM rental price), and (4) “unbundling” (i. e., pricing services separately from the equipment purchase price).
It is no answer to the charge to say that these practices are not “predatory”23 but “honestly industrial”24 — that is, of a kind an ordinary enterprise might utilize with impunity. If the jury concluded IBM possessed monopoly power in the leasing of general purpose computers, IBM would be precluded from employing otherwise lawful practices that unnecessarily excluded competition from the submarket.25 The question is whether the jury could have found that the alleged practices were in fact adopted, and, if so, whether they had the prohibited effect. IBM’s position is that Greyhound failed to show any manipulation of the multiplier or technological discount, and that “unbundling” and the fixed term plan were not exclusionary but pro-competitive.
1. The Fixed Term Plan
IBM had leased mainframe equipment for 90 days and peripheral equipment for 30 days. In May 1971 IBM announced the “fixed term plan,” offering an 8 percent reduction on some peripheral equipment for a one-year lease, and a 16 percent reduction for a two-year lease. The plan also eliminated extra shift and maintenance charges. Substantial penalties were imposed for premature lease cancellation. The purchase price of the equipment was also reduced 15 percent, and purchasers were given a 12 percent technological discount per year for up to two years. At the same time IBM increased rental rates for mainframe equipment.
Greyhound contends that the fixed term plan locked customers into IBM’s rental base and made price competition more difficult. But the record shows that leasing companies had traditionally priced peripheral equipment lower than IBM and offered lease terms of from one to seven years. Greyhound failed to show that IBM’s action with respect to peripheral equipment was *499anything more than a reasonable response to this competition.
Greyhound can hardly complain of IBM’s increase in its rental rates for mainframe equipment, since this change could only work to the advantage of leasing companies.
2. Technological Discount
Although electronic data processing equipment is virtually indestructible, it is nonetheless subject to obsolescence as new technology replaces the old. In recognition of this fact IBM grants a “technological discount” on the purchase price of used equipment. Greyhound alleges that IBM manipulated the technological discount in such a way as to restrict competition from leasing companies.
Until late 1963 IBM’s technological discount on second generation equipment was 10 percent per year, up to a maximum of 75 percent. Thus, equipment on the market for several years could be purchased at 25 percent of original cost. Leasing companies made extensive use of the second generation discount. IBM’s Management Review Committee observed in 1965 that one reason for the rapid growth of leasing companies was their ability to purchase equipment at substantial discounts and return a profit in a short period of time.
In 1963 IBM reduced the annual discount from 10 to 5 percent per year and the cumulative maximum from 75 to 35 percent. In 1964, shortly after the announcement of System 360, the discount was changed to 12 percent after the first year with no further discounts in succeeding years. Thus, the lowest price at which a purchaser could obtain a third generation IBM computer was 88 percent of the original price.
These changes restricted the capacity of leasing companies to compete by inhibiting purchases late in the product cycle. Because reduction of the discount increased the price leasing companies had to pay for their equipment, growth of their inventory was curtailed. Confining the discount to the first year of use required the leasing companies to bunch their purchases in the early years of a product cycle, eliminating the previously profitable practice of acquiring equipment late in its useful life at a relative low and quickly recoverable cost.26
There was evidence from which the jury could infer that these anticompetitive consequences were intended. IBM’s vice president for finance and planning acknowledged that the alter technological discount on the 360 would reduce purchases. The Management Review Committee’s comment in 1965, after the change in the discount schedule, that leasing companies had prospered under the former policy supports an inference that the change was aimed at harming these competitors. IBM’s director of finance noted in 1969 that although a declining purchase price “makes economic sense,” that policy had been rejected in order to create a “potential negative impact on leasing companies through a devaluation of their inventory.”
*500IBM contends that Greyhound carries IBM equipment on its books at a value higher than the equipment would be worth under the technological discount available prior to late 1963, implying that Greyhound’s accounting proves IBM’s original discount rate did not reflect economic realities. However, Greyhound depreciated IBM equipment at the rate of 10 percent per year from the date of purchase, and IBM itself depreciated the equipment over a six-year period. Even if the jury were to find the original discount rate excessive, it could still conclude that the reduction to a total of 12 percent was not economically justifiable.27
3. Multipliers and Maintenance Rates
The “multiplier” — a ratio describing the relationship between IBM’s sales price and IBM’s monthly rental charge — reflects both the cost of the equipment to the leasing company and the rental charge with which the leasing company must be competitive. As the multiplier increases, the number of rental months necessary to recover the cost of the equipment also increases, and investment in the system becomes less profitable. Greyhound’s president testified that the multiplier “dictates whether we can do business or whether we can’t do business, whether our company is viable and whether it isn’t viable.” Even a modest change in the multiplier can have a significant effect upon the ability of leasing companies to compete.
Greyhound contends that beginning with new models of System 360 announced in 1968 (Model 25 and System 3), and continuing through System 370, IBM increased the multiplier substantially, and the effect of this increase was to limit competition from leasing companies.
IBM insists no such increase occurred, and that Greyhound’s contrary assertion is “a flat misstatement of the record.” The record is replete with calculations reaching apparently inconsistent results. The conflict appears to result primarily from the fact that the disputants are referring to different things.
The “gross” multiplier is IBM’s sales price divided by IBM’s monthly rental charge. However, because IBM’s rental charge included the cost of maintenance and leasing companies do not provide maintenance leasing company rates must be competitive with IBM’s rental charge minus IBM’s monthly maintenance rate.28 This ratio of IBM’s sales price to IBM’s rental charge minus the maintenance rate is called the “net” or “effective” multiplier. The multiplier of concern to leasing companies includes one additional adjustment. The IBM sales price must be reduced by the amount of the technological discount or investment tax credit.29 IBM’s failure to take this step into account in calculating the multiplier on System 360 computers explains much of the confusion at trial.
Greyhound’s figures are derived by dividing IBM’s sales price minus the applicable discount or credit by IBM’s rental charge minus the maintenance rate. From the evidence presented at trial the jury could have found that IBM did increase this multiplier. Evidence indicated that when Greyhound purchased its System 360 equipment, the average multiplier, considering all dis*501counts, was 42.5 to 1. But when IBM offered 370 equipment for sale, the multiplier had been increased to 48 to l.30
Moreover, the increase was accomplished at least in part by means inconsistent with the competitive model. There was evidence that instead of lowering rental rates, an action consistent with competitive behavior, IBM increased its maintenance charges despite decreased maintenance costs. Each succeeding generation of IBM equipment was more reliable and hence less costly to maintain. Maintenance costs on 360 computers, for example, were less than those on second generation computers. Although 370 computers represented another marked advance in reliability, IBM raised its maintenance rates on this equipment.31
There was evidence from which the jury could conclude that the effect of the increase in the multiplier was to restrict leasing company access to 370 equipment severely. If leasing companies elected to purchase System 370 equipment, they would have to persuade their customers to enter into seven-or eight-year leases, which most users would reject as unreasonably long. Several witnesses testified that the new multiplier effectively foreclosed leasing company purchases of IBM’s 370 equipment and thus from participation in the business of leasing such equipment in competition with IBM.32
*5024. “Unbundling” of Services
Prior to June 1969 IBM provided certain services to IBM customers without additional charge, including education of customer personnel, software support, technical guidance in the use and application of the equipment, and advice on physical installation. The cost of these services was included or “bundled” in IBM’s rental charge. IBM provided equivalent services to the first users of purchased computers, including leasing company lessees. A Greyhound witness testified that the cost of these services represented about 15 percent of the purchase price.
In June 1969 IBM announced it would no longer provide services to IBM rental customers or to first users of purchased equipment except upon payment of an additional charge. At the same time, IBM reduced its rental charges and purchase prices by 3 percent.
Since IBM did not compensate purchasers for the withdrawal of services, leasing companies that had IBM computers still placed with first users were deprived of services for which they had already paid. In effect, IBM raised the multiplier after the leasing companies had purchased the equipment. Leasing companies were burdened with an inflated investment in equipment already bought and at the same time were compelled to meet reduced IBM rental rates in the leasing market.
In addition, IBM recognized that since the purchaser pays for services at once while the rental customer pays over a period of time, the purchase price should be cut by more than the rental price in order to show an even reflection of the cost of services. However, IBM did not make the purchase price reduction because, as one IBM document stated, it hoped to “protect the level of purchase multipliers to the maximum extent possible.” The jury could thus have concluded that IBM’s method of unbundling effectively raised multipliers on future purchases as well.33
IBM claims that its decision to charge separately for services was pro-competitive because “it opened the door wider to actual and potential suppliers of the same or similar services.” It may have been pro-competitive to charge separately for services and equipment, but it was anticompetitive to do so in a way that left the leasing companies with an inflated investment and lowered returns.
5. General Defenses
IBM argues that its market power rests upon superior technology and business acuity. As the discussion has suggested, however, on the evidence thus far presented at trial the jury could have concluded that IBM maintained its monopoly power in the leasing of general purpose computers in part by practices that unnecessarily, even deliberately, excluded leasing companies from an opportunity to compete. Judge Wyzanski’s characterization of the leasing practice involved in United States v. United Shoe Machinery Corp., 110 F.Supp. 295, 344-45 (D.Mass.1953), aff’d per curiam, 347 U.S. 521, 74 S.Ct. 699, 98 L.Ed. 910 (1954), is equally applicable to IBM’s practices with respect to the technological discount, the multiplier, and the “unbundling” of services:
. [T]hey are not practices which can be properly described as the inevitable consequences of ability, natural forces, or law. They represent something more than the use of accessible resources, the process of invention and innovation, and the employment of those techniques of employment, financing, production, and distribution, which a competitive society must foster. They are contracts, arrangements, and policies which, instead of encouraging competition based on pure *503merit, further the dominance of a particular firm. In this sense, they are unnatural barriers; they unnecessarily exclude actual and potential competition; they restrict a free market.
IBM offers a second general defense. As we have said, Greyhound complains that the challenged practices made it more difficult for leasing companies to purchase IBM’s general purpose computers. IBM points out that Greyhound did not establish IBM had monopoly power in the market for purchase and sale of general purpose computers as distinguished from the market for leasing such equipment. IBM argues that this omission is fatal to Greyhound’s case.
Failure to establish that IBM had monopoly power in the sales market is not a legal bar to holding that IBM violated the Act by using exclusionary sales tactics to maintain its monopoly power in the lease market. The Sherman Act would be violated if IBM had monopoly power in the sales market and used that power to foreclose competition, gain a competitive advantage, or destroy a competitor in the lease market. See Otter Tail Power Co. v. United States, 410 U.S. 366, 377, 93 S.Ct. 1022, 35 L.Ed.2d 359 (1973); United States v. Griffith, 334 U.S. 100, 107, 68 S.Ct. 941, 92 L.Ed. 1236 (1948). But a concern with monopoly power in a relevant market also violates section 2 if it willfully maintains that power. See, e. g., United States v. Grinnell Corp., supra,
384 U.S. at 570-71, 86 S.Ct. 1698. Thus, Greyhound has established a prima facie violation of the Act by showing that IBM employed exclusionary tactics to maintain an existing monopoly in the lease market. United States v. United Shoe Machinery Corp., supra, 110 F.Supp. at 343. See Industrial Building Materials, Inc. v. Interchemical Corp., supra, 437 F.2d at 1344-45.34
Perhaps IBM intends to make a factual argument rather than a legal one — that absent monopoly power in the sales market, IBM could not in fact have fixed the terms and conditions upon which the equipment was sold, as Greyhound asserts, since Greyhound and other leasing companies could simply have turned to another seller to obtain their equipment.
Greyhound offered direct evidence to prove that the conduct complained of did occur and that it restricted the competition of leasing companies in the leasing market, in which IBM possessed monopoly power. This was sufficient to establish a prima facie case. Greyhound was not required to prove the source of IBM’s power to do what Greyhound’s evidence indicated IBM in fact did. Greyhound’s failure to prove that IBM possessed monopoly power in the sales market may have affected the weight of Greyhound’s evidence, but did not render it insufficient to support a verdict.35
*504III. Attempt to Monopolize
IBM argues that the attempt to monopolize charge was properly taken from the jury because Greyhound failed to offer sufficient proof on any of the following issues: (1) “an appropriate relevant market in which IBM could have attempted to monopolize,” (2) “a dangerous probability” of monopolization, (3) “the required specific intent,” and (4) “that any action by IBM was predatory in nature.”
We have held the evidence sufficient to permit the jury to find that IBM monopolized the submarket for the leasing of general purpose commercial computers. Nonetheless, we assume for the purpose of evaluating Greyhound’s claim of attempt to monopolize that we are in error as to the first two issues and that the record would not support a jury finding of even a dangerous probability of monopolization of an appropriate market.
On this premise, Greyhound would still be entitled to go to the jury on the charge of attempt to monopolize if there were sufficient proof on the third and fourth issues. A prima facie case of attempt to monopolize is made out by evidence of a specific intent to monopolize “any part” of commerce, plus anticompetitive conduct directed to the accomplishment of that unlawful purpose. Knutson v. The Daily Review, Inc., 548 F.2d 795, 813-14 (9th Cir. 1976); Twin City Sportservice, Inc. v. Charles O. Finley & Co., 512 F.2d 1264, 1276 (9th Cir. 1975); Trixler Brokerage Co. v. Ralston Purina Co., 505 F.2d 1045, 1051-52 (9th Cir. 1974); Chisholm Bros. Farm Equip. Co. v. International Harvester Co., 498 F.2d 1137, 1144-45 (9th Cir. 1974); Hallmark Industry v. Reynolds Metals Co., 489 F.2d 8, 11-13 (9th Cir. 1973); Moore v. Jas. H. Matthews & Co., 473 F.2d 328, 332 (9th Cir. 1973); Industrial Building Materials, Inc. v. Interchemical Corp., 437 F.2d 1336, 1344 (9th Cir. 1970); Lessig v. Tidewater Oil Co., 327 F.2d 459, 474-75 (9th Cir. 1964).36
If proof of an economic market, technically defined, and proof of a dangerous probability of monopolization of such a market were made essential elements of an attempt to monopolize, as a practical matter the attempt offense would cease to have independent significance. A single firm that did not control something close to 50 percent of the entire market, see Twin City Sportservice, Inc. v. Charles O. Finley & Co., supra, 512 F.2d at 1274, would be free to indulge in any activity however unreasonable, predatory, destructive of competition and without legitimate business justification. Any concern not dangerously close to monopoly power could deliberately destroy its competitors with impunity. These are not abstract hypotheses. A market share approaching monopoly is not required to enable one concern seriously to impede the capacity of others to compete by use of abusive trade practices. A construction of the Sherman Act that would immunize such practices would be contrary to the purposes of the Act; it is not required by the Act’s language or legislative history.37
*505In the present ease the jury could have inferred a specific intent to exclude leasing companies from competition from such evidence as expressions of concern by IBM officials over growing leasing company competition and repeated references by such officials to the goal of limiting sales of IBM equipment and increasing IBM’s lease base, and from the way IBM sought to accomplish this goal. Eliminating the technological discount late in the product cycle despite the reality of technological obsolescence, increasing the multiplier by raising maintenance charges in the face of a reduction in maintenance costs, and separating service charges in a way that inflated leasing company investment while reducing their rental income, appear, prima facie, to be anticompetitive activities that impaired competition without a legitimate business purpose.
Greyhound introduced sufficient evidence to carry the attempt to monopolize claim to the jury.
IV. Damages
Greyhound met its burden of introducing sufficient evidence to permit the jury to infer that Greyhound had sustained damage and that IBM had caused it.38 There was testimony that Greyhound was unable to supplement its inventory with late cycle 360 equipment because of IBM’s reduction of the technological discount, and that Greyhound was virtually foreclosed from purchasing System 370 equipment because IBM raised the multiplier.
An IBM internal memorandum prepared when System 370 was announced supports Greyhound’s contention that IBM is the primary source of Greyhound’s problems. The memorandum summarizes a series of calculations based upon projected multiplier increases consistent with those shown at trial and concludes “the economy will harm the leasing company by an additional 11%.” IBM characterizes the document as meaningless and “wholly speculative,” and urges that it be disregarded. But a jury could infer that the “IBM actions” referred to were the increases in the multiplier and maintenance rates that in fact occurred, and that the writer believed these practices would have the effect of harming leasing companies nearly twice as much as market factors not in IBM’s control.
IBM argues that “[p]erhaps Greyhound Computer is not buying 370 now because . . . it cannot take advantage of the 13% price reduction which is the effect of the investment tax credit.” As the very • phrasing suggests, IBM’s argument presents a question for the jury. Greyhound’s evidence indicates that the benefit of the tax credit was deferred rather than lost. Moreover, given full credence, IBM’s contention does not detract from evidence showing that multipliers on the 370 are considerably higher than those on the 360.
IBM suggests that Greyhound may have been unable to purchase 370 equipment because the system had not been on the market long enough to make the technological *506discount available. But a Greyhound witness testified that because of the increased multiplier, 370 equipment would not be a reasonable investment for leasing even with the discount. It was the jury’s function to choose between the conflicting inferences.
For these reasons we reject IBM’s contention that the evidence was insufficient to permit a jury finding of injury and causation. IBM also insists, however, that Greyhound “only speculates about how much it might have been damaged by any acts of IBM.”
All that is required of the victim of an antitrust violation is evidence showing “the extent of the damages as a matter of just and reasonable inference, although the result be only approximate.” Story Parchment Co. v. Paterson Co., 282 U.S. 555, 563, 51 S.Ct. 248, 250, 75 L.Ed. 544 (1931).39 This standard was satisfied here.
A forecast prepared by Greyhound estimated the company could earn $12 million more in after-tax profit between 1971 and 1975 if it could purchase 370 computers on terms as favorable as those available on the 360. IBM points to testimony of Greyhound’s president that the report was “meaningless.” But the witness’s apparent meaning was only that the accuracy of the report as a forecast had been destroyed by changes in IBM’s pricing practices.
Other evidence in the record would permit the jury to estimate the amount of Greyhound’s damages by applying Greyhound’s profit rate on past business to the volume of business assertedly lost as a result of IBM’s conduct. IBM argues that Greyhound’s profit rate cannot be determined and, in any event, that Greyhound failed to show any similarity between its past business and the future business from which it was excluded.
IBM contends that past profits can only be calculated when the economic life of the particular equipment has ended. Although the purchase price of the equipment is known, IBM argues that the economic life over which it must be amortized is not, and that there is no agreement as to the proper depreciation rates. Further, IBM asserts, both future rental income and future expenses are unknown and highly speculative.
If IBM’s argument were accepted, antitrust damage actions would have only limited and fortuitous application in any business involving long-term capital investment. Whether such a venture will be profitable, and, if so, what the profits will be, is necessarily uncertain until the investment has been fully amortized. The risk that error will occur in resolving this kind of uncertainty must be borne by the antitrust violator where wrongdoing intervenes before the process is complete. Bigelow v. RKO Radio Pictures, Inc., 327 U.S. 251, 265, 66 S.Ct. 574, 90 L.Ed. 652 (1946); Story Parchment Co. v. Paterson Co., supra, 282 U.S. at 563, 51 S.Ct. 248; Eastman Kodak Co. v. Southern Photo Materials Co., 273 U.S. 359, 379, 47 S.Ct. 400, 71 L.Ed. 684 (1927).
Greyhound had an established business and the future profits could be shown by past experience. Eastman Kodak Co. v. Southern Photo Materials Co., supra, 273 U.S. at 379, 47 S.Ct. 400. The only condition to a calculation of damages on this basis is that “the market conditions in the two periods were similar but for the impact of the violation.” Pacific Coast Agricultural Export Ass’n v. Sunkist Growers, Inc., 526 F.2d 1196, 1207 (9th Cir. 1975). As we have seen, Greyhound sought to prove loss of business and consequent damage from two basic courses of conduct: IBM’s failure to grant late cycle discounts on System 360 equipment, and IBM’s manipulation of the multiplier and service charges on System 370 equipment.
It is true that at the time of trial Greyhound’s 360 equipment was still on lease with much of its value not yet depreciated, and that 370 equipment was still new on the market. However, the record afforded a reasonable basis for estimating the economic life of both systems and the loss of profits resulting from IBM’s interference *507with Greyhound's participation in the distribution of both.
Three “generations” of IBM computers are involved in the computation — the second generation introduced in 1958, the third (System 360) in 1964, and the so-called fourth (System 370) in 1970. Greyhound’s profit experience with second generation equipment provides a reasonable basis for computation of damages resulting from Greyhound’s exclusion from late cycle leasing of 360 equipment, and Greyhound’s profit experience in leasing 360 equipment serves as an appropriate basis for measuring Greyhound’s loss resulting from its exclusion from leasing 370 equipment.
There was ample evidence that the economic life span of each of these generations of equipment was about 10 years. The jury could reasonably assume that a straight-line depreciation policy of 10 percent per year was proper, and testimony supported the view that a 10 percent residual value was reasonable. Greyhound’s profit calculations were made on the basis of these assumptions.
Greyhound began purchasing second generation equipment in about the fourth or fifth year of the product cycle, a point roughly comparable to that in the economic life of System 360 when purchases began to decline because no late cycle discount was available. Greyhound invested $48 million in second generation equipment and earned book profits of $4.25 million.40 These profits, made with the benefit of the technological discount, afforded a fair basis for calculating the extent of damages caused by the elimination of the technological discount on System 360.
Greyhound purchased 360 equipment almost exclusively in the early years of its product cycle. These purchases were made prior to IBM’s multiplier increase. Greyhound invested $171 million in 360 equipment, and the expected profit was at least $20 million. These profits, made with the benefit of the more favorable multiplier, afforded the basis for a just and reasonable inference of the amount of damage sustained by Greyhound from its preclusion from early cycle 370 purchases by IBM's manipulation of the multiplier.
Finally, Greyhound introduced testimony that it had planned to invest at least $50 million per year in IBM computer equipment in the years 1969 through 1972, but that it was unable to do so because of IBM’s purchase-restricting practices. Such an annual investment would appear reasonable in light of Greyhound’s investments in 360 equipment. See note 26 supra. Using as a guideline the profit figures Greyhound presented for its $171 million investment in 360 equipment, the jury could have calculated Greyhound’s damages in these years.41
V. Evidentiary Rulings
Greyhound challenges three of the trial court’s evidentiary rulings.
1. Greyhound contends that the trial court erred in modifying an earlier ruling of the judge designated pursuant to 28 U.S.C. § 1407 to preside over the pretrial and discovery proceedings in this case. Greyhound asserts that an order of the pre*508trial judge required IBM to object by a given date to the admission of documents obtained by discovery, that IBM waived its right to object on the ground of hearsay by failing to make such an objection by the date fixed, and that the trial judge erroneously permitted IBM to raise the hearsay objection at trial.
One district judge in a multijudge court may modify the interlocutory order of another for “cogent reasons.” The question on review is whether the second judge abused his discretion. United States v. Desert Gold Mining Co., 433 F.2d 713, 715 (9th Cir. 1970); Tanner Motor Livery, Ltd. v. Avis, Inc., 316 F.2d 804, 809 (9th Cir. 1963); Castner v. First National Bank, 278 F.2d 376, 380 (9th Cir. 1960). Greyhound has not indicated what the excluded documents were, what they contained, or what they would prove. It has demonstrated no prejudice, simply asserting without particularization that it was forced to alter its strategy at trial. On the basis of this showing, we decline to hold the trial judge abused his discretion.
2. The district court excluded all reference to a consent decree entered into between IBM and the United States in settlement of antitrust litigation, some 20 years ago. The decree required IBM to abandon its prior “lease only” policy and offer its computers for sale, and included other provisions that contributed to the establishment of leasing companies. Determining whether such a decree should be placed before the jury requires a balancing of probative value against prejudicial impact, a task committed to the discretion of the trial court. Control Data Corp. v. IBM Corp., 421 F.2d 323, 326 (8th Cir. 1970). See generally City of Burbank v. General Electric Co., 329 F.2d 825 (9th Cir. 1964). In this case, as Greyhound candidly admits, striking the balance “is a close question.” We are unable to say the trial court abused its discretion in resolving it as it did. There is merit, however, in Greyhound’s contention that IBM’s opening argument suggests that the trial judge must be alert to protect Greyhound from arguments that may mislead the jury unless the jury is informed of the decree and its terms.
3. Finally, Greyhound objects to rulings by the trial court precluding testimony as to manufacturers that have gone out of business. The rulings did not prejudice Greyhound since the desired testimony was later admitted.
VI. Breach of Contract
We agree with the district court that Greyhound’s separate claim that IBM breached a contractual obligation to provide services to first users of IBM machines was not supported by sufficient evidence to carry it to the jury. Viewed most favorably to Greyhound, the evidence showed only that some unspecified customers had bargained on an individual basis for some unspecified allotment of only generally defined services, and that some undetermined portion of these services had been withheld.
Affirmed in part, reversed in part, and remanded for further proceedings in accordance with this opinion.