Opinion by
Mr. Justice Potter,Counsel for appellants in this case say that the assignments of error raise two questions:
1. Was the offer of defendants to introduce testimony of delay on the part of plaintiff in completion of the Annex Hotel building, competent under rule 8 of the Allegheny county courts, requiring notice prior to the trial in case defendant proposes to introduce proof of set-off or counterclaim?
2. Had the defendants a right to explain what they claim to be ambiguous provisions of the contract sued upon, and the right to define and limit, by parol testimony, the powers of their architects in the approval of what was known as the “revised plans”?
*465With regard to the first question, the trial judge based his ruling, excluding evidence of the claim for damages on account of delay in the completion of the work, upon the failure of defendant to comply with the provisions of rule 8 of the Allegheny county common pleas courts. Section 3 of the rule provides: “This rule shall apply to a specification and statement of set-off filed by defendant who shall within fifteen days after filing the same, notify the plaintiff thereof, and the plaintiff shall, within fifteen days after notice thereof, file his reply thereto, verified by affidavit.”
The provision of the rule here in question has been before this court in at least three cases. In Bair & Gazzam v. Hubartt, 139 Pa. 96, the suit was upon a contract, and in the affidavit of defense it was alleged that the work had been done in a way that increased the cost, and impaired the value to the defendant, and a deduction was claimed upon that account. It was held that sec. 3 of the rule applied to a counterclaim of the kind set up.
On appeal, the judgment was affirmed by this court, Justice Mitchell saying (p. 99): “It is argued that this part of the defense was not set-off, but failure of consideration, admissible in evidence under the general issue, and therefore that the rule of court was not applicable. But whether it was a technical set-off, or a defalcation under the broader practice of this state, or merely failure of consideration resulting in an overpayment, which defendant sought to get back, is not at all material. In any aspect, it was a counterclaim by defendant against plaintiffs. The object of the rule of court is manifestly to reduce the contest at the trial to the points actually in dispute, and whenever any matter sought to be introduced at the trial, called by whatever name it may be, is such as to require notice to the other side, the object of the rule would seem to demand its application. The defense, as already said, was a counterclaim, which certainly in substance partook of the nature of a set-off, and might well be held to be within the meaning of the term as used in the rule. Whether or not it should be so construed was peculiarly for the court below; and all our cases agree, that upon a question of the construction or *466application of its own rules, a court can be reversed only for manifest and material error.”
And in Higgins Carpet Co. v. Latimer, 165 Pa. 617, Chief Justice Sterrett said (p. 623): “It is not a sufficient answer to say that the defense was not set off and therefore the rule was not applicable. The first item of defense, as we have seen, is clearly a counterclaim for damages resulting from refusal to deliver certain pieces of carpet, etc. It may be that in the technical sense of the word the other items are not strictly 'set off/ but the rule was never intended to have any such restricted meaning. It was meant to embrace every species of counterclaim that under our more liberal practice may be legally or equitably interposed as a defense.” And on p. 624: “As a means of promoting justice and expediting the trial of causes, the rule under consideration has proved to be most valuable; and its usefulness and efficacy should not be impaired by neglecting to enforce its provisions on all proper occasions.”
In Organ Company v. Ecker, 184 Pa. 350, in answer to the suggestion that filing the statement of set-off, without more, was notice to the plaintiff, it was pointed out that the rule positively and plainly requires both filing of the statement and notification thereof to the plaintiff. We need add nothing further to these citations of authority. The rule in question has been tried and tested, and found to work well in the courts of the county from which this appeal comes. The exclusion of evidence by means of a general rule, may in particular instances work injustice, but any such occasional result is overbalanced by the stability which the general operation of the rule maintains. As to the interpretation and application of the rule in this instance, we see no reason to interfere. As our Brother Mestrezat said in Webster v. Coal & Coke Co., 201 Pa. 278 (281): “We have repeatedly said that a court is the best exponent of its own-rules, and that this court will not reverse for any construction, unless it is manifestly erroneous and injurious.”
As to the second question raised by appellants, under the assignments of error, with respect to the rejection of offers of *467parol testimony to explain an alleged ambiguity in the written contract, we do not see that there was any ground for the admission of the proposed evidence. It seems that plans and specifications had been prepared, upon which plaintiffs submitted an estimate. The estimated expense of building according to the original plans being greater than the company desired, certain alterations were made to reduce the cost, and' revised plans and specifications were prepared by the architects. The contract contemplated the erection of the building according to these revised plans, and it was so erected, and the work was approved by the architects. The offer of defendants practically was to show that the new plans required less steel; that the architects were not authorized to draw the plans in that way, and that plaintiff should be compelled to make an abatement of the contract price, to the extent of the lessened amount of steel needed. We do not see that the evidence offered explains any ambiguity in the contract. There was no question between the parties as to the meaning of the term “revised plans and specifications.” It referred to the new plans, etc., to be prepared by the architects, employed by the hotel company. The allegation is that the architects did not prepare such plans in the way their employers directed and authorized. But if so, it was not the fault of the plaintiff. The steel company had a right to rely upon the plans given to it by the architects who represented the hotel company. The contract provided that this work should be done according to the revised plans, and to the satisfaction of the architects and building managers. The work was so done, and the plaintiff was apparently entitled to receive the stipulated price. We can see no reason why the plaintiff should have supplied more steel than the contract, called for, or why it should have departed in any way from the plans, in erecting the building. It was entitled to rely upon the apparent authority with which the defendant had clothed the architects.
The trial judge was right in rejecting the offers of evidence intended to vary the terms of the written contract, and in directing a verdict for the plaintiff.
The judgment is affirmed.