Wheeler, J.

The motion to correct the finding is not supported by the evidence. The supplementary agreement was not found without evidence. Mr. England, in behalf of the plaintiff, testified that the parties agreed upon a method for determining what should constitute first orders, and his testimony was corroborated by certain of the exhibits. There was evidence that the items claimed as first orders were such. Mr. Blakeslee testified for the defendant that none of these orders were filled until the defendant had investigated the financial standing of those to whom goods were to be shipped under orders sent defendant by plaintiff. He also testified: "We always looked up whether we had sold them before or not, in order to get a line on what their financial standing was first of all.” The defendant never notified the plaintiff that any of these orders were not "first orders.” From this, in connection with the fact that defendant never notified plaintiff that the orders sent in were not first orders, the inference, in the absence of contradictory evidence, followed that *320 the orders were first orders and from concerns not before selling Skat.

The defendant was not entitled to a finding that it could not be determined from the books of account kept by it that the concerns from whom orders had been taken had not before been selling Skat. The evidence upon this point was conflicting. In addition, the court was amply justified in finding that the parties had agreed that the information to be found upon the defendant’s books was conclusive as to this matter. The books were in its possession. The defendant never notified the plaintiff that the orders sent in were not first orders. The inference was warranted that the orders so accepted and filled were first orders. The evidence of the defendant’s witness was contradictory as to whether the books would show whether the concerns, for which orders sent in by the plaintiff had been filled, were “concerns.not now selling Skat.” This was a fact which in the ordinary course of bookkeeping should have appeared upon the books. We think the court was right in refusing to find that it did not so appear.

Errors assigned upon rulings on evidence are limited in argument to one point. The written contract in effect provided that the plaintiff should furnish orders for Skat, which the defendant should fill, “from financially responsible concerns not now selling same.” The court permitted proof, by an oral agreement between the parties made subsequent to the written contract, of a method of determining what should be considered first orders from “financially responsible concerns not now selling same.”

It is urged that the written contract is thus permitted to be varied by parol. This is a misunderstanding of the purpose of the evidence. It was an attempt to provide a method of determining one of the provisions *321 of the contract, the determination of which the contract left open. The trial court properly characterized it: “It is,” the judge said, “evidently an arrangement made concerning the execution of the contract, the method of execution, not the changing of any terms.” The supplementary understanding is not to the disadvantage of the defendant. It leaves the decision of what are “first orders” to the books of the defendant. If the customer procured by the plaintiff was among the customers appearing upon the books of the defendant, it was not a new order; if it did not so appear, it was. This oral agreement, leaving the settlement of which were first orders and leaving the decision of the financial responsibility of the customers to the defendant, was manifestly fair to the defendant. The sense and meaning of the language used in a contract, or its application to the surrounding circumstances, may be ascertained by evidence dehors the contract, since in no other way can the intention of the parties be so certainly ascertained. In re Curtis-Castle Arbitration, 64 Conn. 501, 514, 30 Atl. 769. So when the contract provides for the ascertainment of a given fact without providing a method for such ascertainment, a subsequent agreement upon such a method does not vary nor add to the terms of the contract, but is rather an agreement supplementary or collateral to the contract, controlled by its consideration and furnishing a means of carrying out one of its terms. It may be established by parol. It is a means of enforcing a provision of the contract in accordance with the agreed wishes of the parties. Agreements of that sort are not within the statute of frauds.

The defendant’s final assignment of error is its claim that the judgment is based upon a wrong measure of damages. The defendant claimed upon the trial, that if the issues were found in favor of the plaintiff it could *322 recover as damages only the amount of “first orders” from “financially responsible concerns not selling” Skat, less any payments made by the defendant to the plaintiff. The issues were found for the plaintiff. Hence that part of the recovery ($219.31) comprising the difference between the amount of the first orders, $542.14, and the payments made, $322.83, is, the defendant admits, properly within the judgment. Excluding the element of interest, the court found due on the contract, and rendered judgment for, $349.17, the balance of the contract price. So that the amount of the judgment which it is claimed resulted from the application of a wrong theory of damages, is $129.86.

The plaintiff, so far as it could, has fulfilled its part of the contract. After the defendant declined to make further performance, the plaintiff ceased to make efforts to secure “first orders.” It was legally justified in this course. Upon the defendant’s breach, it became liable for such fair compensation as was reasonably within the contemplation of the parties; and this was the reasonable profits of the contract. Haynes & Co. v. Nye, 185 Mass. 507, 509, 70 N. E. 932. The trial court held the measure of damage to be the contract price. In some instances it might be. In this case we do not think it is.

It does not follow that there must be a new trial because of this ruling. It appears from the finding that there was no expense which the plaintiff was under in continuing this advertisement after the breach, hence, if that were the only factor to be considered, the contract price would measure the profits. But as a part of the expense to the plaintiff was the securing of first orders, this expense should be deducted in order to get at the true profit. No evidence was offered and no claim made by the defendant as to this. Had this been an item of any considerable-size, it is possible it would *323 have appeared in the case. Its maximum amount, as we read the record, must have been inconsiderable, and the omission from the record of its exact amount does not materially prejudice the defendant. Under these circumstances a new trial ought not to be granted to correct a judgment reached upon the application of an erroneous measure of damages, when that correction will involve, at the most, a sum inconsiderable in amount.

There is no error.

In this opinion the other judges concurred.