Parsons, C. J.

The rule “which forbids the admission of parol evidence to contradict or vary a written contract is not infringed by any evidence of known and established usage respecting the subject to which the contract relates. To such usage, as well as to the lex fori, the parties may be supposed to refer, just as they are presumed to employ words in their usual and ordinary signification. . . . Proof of usage is admitted, either to interpret the mean *279 ing of the language of the contract, or to ascertain the nature and extent of the contract, in the absence of express stipulations.” 1 Gr. Ev., s. 292; 4 Wig. Ev., s. 2440. “The liberal rule ... is today conceded, practically everywhere, to permit resort in any case to the usage of a trade or locality, no matter how plain the apparent sense of the word to the ordinary reader.” 4 Wig. Ev., s. 2463 (2); George v. Joy, 19 N. H. 544, 546; Swamscot Machine Co. v. Partridge, 25 N. H. 369, 378. See Glover v. Baker, 76 N. H. 393, 415.

The evidence offered by the plaintiffs of the custom or usage to make final settlement for cutting, sawing, etc., according to the surveys of lumber made at the time of its sale was competent and should have been admitted. It tended not to contradict, but to make intelligible, the written contract. If proved as a fact within the minds of the parties when the written engagement was entered into, it. tended to show what they meant by what they said. The agreement of the defendant “to guarantee the amount of lumber he receives pay for” implies that on some basis of measurement payment might be made, leaving the accuracy of the measurement to be determined at some future time. The evidence tended to show how the parties understood this determination should be made. When made, the defendant’s guaranty applied. It is not seriously contended that the evidence was incompetent, but the contention is that the findings of waiver and laches render the construction of the written contract immaterial. But the evidence bore directly upon the question whether what was done in the way of measurement and payment while the sawing was going on was understood as a final settlement, or as a preliminary adjustment to be corrected later under the contract. It also tended to show when in due course it could be ascertained whether the measurement for which the defendant had been paid was erroneous, and hence was material upon the question whether the plaintiffs unreasonably neglected to make claim after they knew or ought to have known of the error.

The referee having found a general verdict for the defendant, states the facts proved before him. It appears that the plaintiffs’ claim was based upon the defendant’s covenant under seal. The bond and its breach found by the referee are facts inconsistent with the general verdict for the defendant, unless facts are found authorizing the conclusion that, despite the breach of the defendant’s covenant under seal, he is not liable in damages therefor. The referee finds that the plaintiffs delayed unreasonably in asserting a *280 claim under the guaranty, and that by the way the plaintiffs dealt with the defendant and his subcontractor in making payments as stated by him, they waived the guaranty. Since the evidence which was wrongfully excluded was material upon each of these propositions, it is unnecessary to consider whether the evidentiary facts stated authorize the finding of waiver, or whether unreasonable delay in asserting a claim under the guaranty would' of itself estop the plaintiffs from their present claim.

Plaintiffs’ exception sustained: report set aside.

All concurred.