ROSS, C. J.
The action is to recover for a No. 1 United States Cream separator and other property to be used in setting up and propelling the separator at Plainfield, Vt.,
“And guaranteed to do as good work as any other sepai’ator in the market and to skim to one-tenth of one per cent, of fat or less; and to skim of summer milk twenty-two hundred pounds per hour and of winter milk eighteen hundred pounds per hour — the machine to be properly operated. By ‘properly operated’ it shall be understood to mean that the machine shall be run at a speed of seventy-two hundred revolutions per minute, and operated in every way in the same manner as usual in the ordinary method followed in the course of separating each day.”
The separator was to be tested and to continue for thirty days to do the work guaranteed under the conditions described. The issue was whether the separator answered the guarantee.
I. The plaintiff gave testimony that, at the time the contract was signed, he explained that by the term “in the usual and ordinary method” as regards the temperature of the milk was meant eighty to ninety degrees in winter and seventy degrees on an average in summer. This testimony was admitted against the exception of the defendants. It opened the door for them to give evidence of what was said on the sub*438ject on that occasion. Nor was any of the testimony excepted to, given by them, outside the scope of the subject opened by the plaintiff. It only gave the reason they had for insisting as they say they did that the term must mean at seventy to seventy-two degrees. The contract and evidence furnish another ground on which the defendants had the right to have the separator operated with the milk at seventy or seventy-two degrees in the winter. It was guaranteed to do as good work as any other separator in the market. The Alpha Separator was then in the market, and the main competitor of the separator in contention. The evidence tended to show that that separator did good work in the winter, when operated with the milk at this temperature, and that the cream thus produced made a better quality of butter. Hence, the defendants had a right to have it tested with the milk at this degree unless the term “in the usual and ordinary method” was to restrict the guarantee as claimed by the plaintiff’s testimony. The charge on this testimony cannot be complained of by the plaintiff. By this testimony the plaintiff asked to have its guarantee limited by the construction, which it said would be placed on these words, to a test with the milk at eighty to ninety degrees in the winter when compared with the Alpha. If the admission of this testimony was an attempt to read into the contract something that was not there as contended by the attorney for the plaintiff, it was allowed at the asking of the plaintiff. The exceptions do not raise the question whether this testimony of the plaintiff was properly admitted and that question is not considered.'
II. The plaintiff excepted to testimony admitted to show the power and fuel required to operate the separator as compared with the same required to operate the Alpha. He contends that the guarantee “to do as good work as any other separator in the market and to skim” etc., relates not to the economy or expense of doing the work, but to its *439quality, or that it would skim as much milk and as clearly of fat as any other separator on the market. The subject matter of the contract was the sale of the separator. The guarantee was with reference to its value when compared with other separators then in the market. It was not the intention of the defendants in requiring, nor of the plaintiff in giving the guarantee to bind the defendants to keep and pay for the separator, if by the test, it was found that it skimmed the milk as clearly of fat and did the work as rapidly as any other separator in the market, but at much greater expense. It was intended that by the guarantee the defendants should secure a separator as good or valuable, everything being considered, as any other in the market, and one which fully ■met the requirements expressed in the guarantee. When the subject of a contract is the sale of a machine guaranteed to do as good work as any other like machine in the market the value of the machine when compared with other like machines depends upon whether it can do the same amount and quality of work at the same expense. If it cannot it does not do as good work within the meaning intended by the parties as the other.
III. On the day before the contract in contention was made, the parties thereto made another conditional sale and purchase of another No. i United States Cream Separator to be set up and tested by the side of the Alpha Separator in the defendants’ factory at Montpelier. The two separators conditionally sold by the plaintiff to the defendants were in every respect alike and were set up and operated very nearly concurrently, and were to be tested by the same agents of the plaintiff. The defendants’ testimony tended to show, that it was understood between the parties, that the tests between the two separators bargained for by the defendants, and the Alpha should be made at Montpelier, as that was the only station where there was an Alpha with which to compare the workings of the machines, when stand*440ing side by side. If this understanding was established, it made the comparisons between the United States Separator at Montpelier and the Alpha pertinent testimony on the question whether the separator in question would answer the guarantee of the plaintiff, that it should do as good work as any other separator in the market. If this understanding should not be established, inasmuch as the United States Separator in contention was identical in construction and size with the one at Montpelier, the working of the latter, when compared with the working of the Alpha under like conditions, was admissible upon the question whether the separator would answer the guarantee, or do as good work as the Alpha. The action of the plaintiff made the use of this class of testimony the more necessary. It refused to make the test called for by the contract because the defendants insisted as they had the right to, unless the guarantee was limited as claimed by the plaintiff by what was said at the time the guarantee was given as shown in point one — that the test should be made with the winter milk at about seventy-two degrees. With this understanding established the agents of the parties, who made the tests of the two separators at Montpelier, were their agents with reference to the test of the Plainfield separator when compared with the Alpha, and their declarations and admissions, made within the scope of their agency, in regard to the tests of the separators at Montpelier, were the declarations and admissions of the parties, not only in regard to the separator at Montpelier, but also in regard to the separator at Plainfield as compared with the Alpha at Montpelier. As no exceptions were taken to the charge of the court in regard to the use which the jury were to make of this testimony it is to be assumed that the court gave the proper and necessary instructions on the subject. None of the declarations and admissions of the agents of the plaintiff who made the tests between the separators at Montpelier admitted so far as brought to our attention were outside the scope of their agency.
*441IV. George R. Remington was one of the plaintifF’s agents who made the tests between the separators at Montpelier. While those tests were being made the plaintiff’s manager wrote him a number of letters and sent him telegrams giving him directions and instructions in regard to making the tests and in regard to substituting another United States Cream Separator of a new and different construction, in some respects, from the one which the plaintiff had conditionally sold and placed on trial there. . These were produced and given in evidence by the defendants. The exception to their admission taken by the plaintiff on the trial is not now insisted upon. To these telegrams and letters Mr. Remington replied. These replies were in the hands of the plaintiff. They tended to support the contentions of the defendant in regard to the issues raised in the trial before the jury. Against its exception, the court ordered the plaintiff to produce them for the inspection and use of the defendants. The plaintiff contends that the court had no power to make this order. By V. S., 1,410, it is enacted:
“The supreme and county courts may in the trial of actions at law on motion and due notice thereof given, require the parties to produce books or writings in their possession or power, which contain evidence pertinent to the issue or relative to the actions where they might be compelled to produce the same by the ordinary rules and proceedings in chancery.”
The reniainder of the section does not relate to the power conferred. On the authorites cited by the plaintiff, (Daniels Ch. Proc. 579, 5th ed. ; Haskell v. Haskell, 3 Cush. 542 ; Wilson v. Webber, 2 Gray 558 ;) the court of chancery has power to compel a party to discover and produce any book or writing which is in his possession or power, and which is material for the establishment of the issues to be established by the orator. The orator by a bill of discovery cannot compel the production of books or writings which are only evidence to establish the defendants’ contentions. The de*442fendant in a bill of discovery is called upon to make answer to the claims of the orator set forth in his bill, but cannot be called upon to produce the written evidence which he relies upon to support his answer. His conscience cannot be probed for that purpose. But if he has in his possession or power, any books or writing relevant to the rights of the orator set forth in the bill, it is against good conscience and equity that he should withhold the same from the orator, and he can be compelled to discover and produce them. If the jury should find, as the defendants’ testimony tended to show, that the tests between the United States Cream Separator and the Alpha at Montpelier, by the agreement of the parties, were to be tests between the separator in contention and the Alpha, then the telegrams and letters ordered to be produced and admitted, were relevant and material to the issues made by the testimony. They were sent and written in reply to the telegrams'and letters of the plaintiff, through its officers and agents, Northrop and Williams, which it is now conceded by the plaintiff were properly received in evidence, and were necessary for a proper understanding of the latter, and also tended to contradict Williams’ testimony, that he did not attempt, secretly, to have United States Cream separator B. substituted for the United States Cream Separator A. at Montpelier, and also in that he was not endeavoring to charge the failure of the latter to stand the test with the Alpha upon the witness Remington.
V. There was no error in the extent of the cross-examination of J. H. James. The interest of a witness, audits extent, may always be shown to be considered by the jury in weighing his testimony. The limits of such cross-examination are somewhat within the discretion of the court. It is never error to allow, by cross-examination, a full and fair-development of the witness’ interest. We do not say it would have been error to have excluded the inquiry in regard to the amount of commission which the witness received while in the *443plaintiff’s service. But it was not error to allow the inquiry and admit the answer.
VI. The remark of the defendant’s attorney, when cross-examining the plaintiff’s manager, to which exception was taken, was provoked and called out by the uncalled for personal declarations of the witness. At most it was only the statement of the attorney’s views of the construction- to be placed on the correspondence referred to. It were better, if it had not been made, as the attorney now concedes. Under the circumstances, of which the jury were cognizant, it was not erroneously prejudicial to the plaintiff. This disposes of the exceptions now relied upon.
Judgment affirmed.
Taft, J., being absent in county court, did not sit.