Relying on the “best evidence rule,” defendants argue that part of the plaintiff’s testimony was improperly admitted. This reliance is misplaced. Plaintiff was allowed to testify, over objection, to the number of men he probably used on the job, the actual footage of pipe used, and the number of hours spent grading. These facts, and others, had been recorded by plaintiff in small notebooks as the job progressed, and after the bill was prepared the notebooks were thrown away. Defendants contend that plaintiff should have been required to produce the notebooks where plaintiff kept track of these figures, rather than testifying to the facts himself. The “best evidence rule,” however, requires the production of a document “only where the contents or terms of [the] document are in question.” 2 Stansbury’s N.C. Evidence § 191 at 103 (Brandis Rev. 1973). Here not the contents of the notebooks, but facts about plaintiff’s work which were within *702plaintiff’s own knowledge are in issue. “[I]f a fact has an existence independent of the terms of any writing [as is the case here], the best evidence rule does not prevent proof of such fact by the oral testimony of a witness having knowledge of it. . . .” Id., n. 24. See also Whitehurst v. Padgett, 157 N.C. 425, 73 S.E. 240 (1911).
 Defendants also assign error to the admission of plaintiff’s testimony that it is the custom in the contracting business for “cut sheets” to be furnished and paid for by the owner of the land, not the contractor. Defendants argue that such evidence would not be admissible to add a new element to a contract. Defendants rely on Lewis v. Salem Academy & College, 23 N.C. App. 122, 208 S.E. 2d 404, cert. denied 286 N.C. 336, 210 S.E. 2d 58 (1974), for this proposition, but that case is not on point. The court in Lewis had before it an express written contract, the terms of which plaintiff attempted to contradict by evidence of the “usual and customary practice” of Salem College. Here we are concerned with an oral contract, and there is no evidence that “cut sheets” were considered by the parties at the time the contract was made. (Defendant testified that after he “thought everything was settled,” plaintiff “came up one day and said we were going to have to have some cut sheets before he could start work. I didn’t know what he was talking about.”) This Court in Lewis quoted 55 Am. Jur., Usages & Customs § 31 at 292, for the proposition that “[a] custom or usage may be proved ... to annex incidents to the contract in matters upon which it is silent.” Lewis v. Salem Academy & College, supra at 128, 208 S.E. 2d at 408. We believe that the challenged testimony here was admissible to prove a matter upon which the contract is silent.
 Error is also assigned by defendants to the denial of their motions for directed verdict or judgment notwithstanding the verdict. On such motions the evidence is to be taken as true and considered in the light most favorable to the plaintiff, Farmer v. Chaney, 292 N.C. 451, 233 S.E. 2d 582 (1977), and the motion should not be allowed unless it appears as a matter of law that plaintiff cannot recover upon any view of the facts which the evidence reasonably tends to establish. Manganello v. Permastone, Inc., 291 N.C. 666, 231 S.E. 2d 678 (1977). Defendants argue that the plaintiff’s evidence was too speculative to go to the jury, since he relied upon his memory rather than written records in testifying to the value of his services. The plaintiff’s *703evidence showed, however, that he submitted a final bill for $66,885 and that he installed 4700 feet of force main at $4.00 per foot, 3060 feet of 4-inch sewer pipe at $4.50 per foot, a lift station for $8700, 27 P-traps at $125 each, 146 feet of storm drainpipe at $8.00 per foot, a manhole for $650, and a catch basin and grate for $100. There was equally specific evidence of other charges. This assignment of error is untenable.
 We likewise find no error in the denial of defendants’ motion for a new trial, though defendants argue that the damage award was a compromise verdict which should have been set aside. The trial court charged the jury that if they accepted plaintiff’s view of the contract they should award him the reasonable value of his materials and services, while if they accepted defendants’ view they should not award plaintiff more than the balance unpaid on $44,000. The jury determined that defendants requested plaintiff to provide materials and services in addition to those included in the agreement, and awarded plaintiff $20,661. This amount comports neither with defendants’ contention of $9,165.60 due to the plaintiff nor plaintiff’s contention of $33,283.13 due him, but it need not be set aside as a compromise verdict simply on that basis. There was much testimony as to which materials and services allegedly were requested after the making of the agreement, and the prices plaintiff charged for them. It was the function of the jury to determine which of those materials and services actually were outside the agreement, and how much was due plaintiff for them. The jury has performed this function, and there is no basis for setting the verdict aside.
We find no error in the trial court’s charge to the jury, or in the other assignments of error defendants bring forward. While the evidence here may not compel the verdict reached, the jury has made its decision, and we can find
Chief Judge MORRIS and Judge CLARK concur.