MR. JUSTICE HOLLOWAY
delivered the opinion of the court.
In this action, plaintiff seeks to recover commissions alleged to be due upon the sale of three automobiles, under the following written agreement:
“This agreement made and entered into this 5th day of May, 1913, by and between H. B. Blair, of Livingston, and B, G. *534Brockway, of Billings, Montana, as follows: The said first party agrees to furnish Reo automobiles for the said second party to sell in Yellowstone and Carbon counties in the following manner: The said second party to get fifteen per cent (15) of sales. Said first party to furnish all automobiles on deposit of one hundred dollars ($100.00) each, at time of order. All orders and specifications to be in Lansing ten days prior to shipment.
“H. B. Blair,
“First Party,
“By R. H. Bishir,
“B. G. Brockway,
“Second Party.”
The circumstances under which a ear was sold to Allard, one of the purchasers, will illustrate the three sales involved in this controversy. Cettergren was Brockway’s agent at Laurel, and Bishir and Green were Blair’s agents who worked to some extent in that vicinity. Cettergren testified that he made several trips to see Allard concerning the sale to him of a Reo car; that he demonstrated the car to Allard several times; that he took Bishir to Allard, and Bishir demonstrated the car to him; that afterward and on the day Allard expressed his intention to purchase a car he introduced Green to Allard; that a sale was then completed by Green, who delivered the car to Allard. On cross-examination, the witness said: “I know that Mr. Green would not have sold the car if it hadn’t been for me, and I think I would have sold the car if it hadn’t been for Green. Mr. Al-lard said he was ready to buy a car before Mr. Green spoke to him.” From the fact that a general verdict was returned in favor of plaintiff, we must assume that the jury accepted this testimony as true, so far at least as it tends to disclose the part which Broekway’s agent played in effecting the sale. It is apparent that the efforts of Cettergren alone did not produce the sale, neither did the unaided efforts of Blair’s agent effect it. The sale resulted from their combined efforts.
*535[1] *534Upon the theory that the agreement does not in terms expressly cover the case, the court permitted evidence to be intro*535duced to the effect that it was understood by both parties, at the time the contract was executed, that Brockway was not expected to go out and complete the sales by his own unaided efforts; that if it was necessary for him to have the assistance of Blair’s agents in the community to close or complete a sale, such assistance would be furnished as a part of Blair’s obligation under the contract; and that this understanding was carried into effect in making the sales which furnish the foundation for this controversy. The admission of this evidence is specified as error — as violating the provisions of sections 5018 and 7873, Revised Codes, which, so far as applicable here, are to the effect that, when the terms of an agreement have been reduced to writing by the parties, no evidence is admissible of the terms of the agreement other than the contents of the writing itself. “The full substance of the evidence admitted” is not quoted as required by Rule X, subdivision “b,” of the rules of this court (123 Pac. xii), and the attention of counsel is directed to the fact that these rules are to be honored by their observance — not by their breach.
It is the contention of appellant that, under the terms of the agreement, Brockway was not entitled to any commission unless and until he made a sale complete in itself or made a contract of sale under which Blair could maintain an action for damages in ease the prospective purchaser failed or refused to take the car. In other words, it is appellant’s contention that the terms of the contract are explicit; that they interpret themselves and leave no room for the application of rules of construction or the introduction of evidence explanatory of the circumstances under which the agreement was made.
*536[2] *535If the sale had been made by the unaided efforts of Brock-way or his agent, there could not be any question of plaintiff’s right to the commission. If the sale had resulted from the unaided efforts of Blair’s agents, Brockway could not lay claim to the commission, for the contract did not give him exclusive territory. But what are the rights of the parties under the contract as they apply, or can be made to apply, to the Allard *536sale? Sections 5018 and 7873, above, refer to contracts complete in themselves and free from ambiguity and uncertainty. Sections 5025, 5030, 5036 and 5038 provide rules of interpretation where the terms of the agreement fail to explain themselves fully or are ambiguous or uncertain. If the language of the agreement is clear and expresses the intention of the parties explicitly, it needs no interpretation (Ming v. Pratt, 22 Mont. 262, 56 Pac. 279); but, if it is not clear and free from ambiguity, then the attendant circumstances under which the contract was made may be examined to furnish a key to the intention of the parties (Alywin v. Morley, 41 Mont. 191, 108 Pac. 778; Quirk v. Rich, 40 Mont. 552, 107 Pac. 821),. We are not prepared to agree with counsel for appellant that the meaning of the language of this agreement is so far free- from doubt that it can be said as a matter of law that it furnishes its own interpretation. That the writing does not contain all the terms of the agreement is apparent at once. Neither the price at which the cars were to be sold nor the terms of sale are specified. Certainly, it was not intended that Broekway might fix any price upon the cars or any terms which would suit him or better enable him to sell them. It is uncertain, too, whether Brockway was to order cars from Blair or directly from the factory. Indeed, the writing appears to be nothing more than a brief memorandum of certain points of their agreement, and the court ruled correctly in admitting the evidence.
Upon the facts found, Brockway was entitled to his commission upon these sales, for the parties had agreed that such assistance as was given him was due to him under the contract.
[3] The second assignment is that the court erred “in giving defendant’s instruction No. 2yz.” The instruction is not set out as required by Rule X, subdivision “b.” The defendant below is the appellant here, and we would be justified in refusing to consider the assignment because of this violation of the rule, or we might content ourselves with saying that a party will not be heard to complain of the action of the court in giving an instruction which he requests; but waiving the failure *537to observe the rule, and assuming, from the argument presented, that fault is found with plaintiff’s offered instruction No. 1, given as instruction No. 4, and that the reference to defendant’s instruction No. 2% is merely an error, it is to be observed that, if instruction No. 4 stood alone and was the sole criterion for determining the circumstances under which plaintiff would be entitled to commission upon a sale in the making of which he received assistance from defendant, then there would be ground for appellant’s complaint. The phrase, “was instrumental in making any sale,” conveys practically no meaning.
[4] It is too indefinite to be of service to the jury in applying the evidence; but one particular paragraph of the entire charge cannot be segregated from the rest. Every paragraph is to be read with the context, and all the instructions considered together as constituting the single charge of the court. (Stephens v. Elliott, 36 Mont. 92, 92 Pac. 45; Michalsky v. Centennial Brewing Co., 48 Mont. 1, 134 Pac. 307.)
[5] At the instance of defendant, the court gave the following instruction: “You are instructed that, in order for the plaintiff to recover by reason of any sale being made by him, you must find that the plaintiff was the moving cause of the sale being effected, and that the sale would not have been made had it not been for the solicitation and efforts of the plaintiff.” The court intended, and the jury must have understood, that these two instructions should be considered together as stating the circumstances under which the plaintiff would be entitled to the commission even though he received assistance from the defendant or his agent in completing the transaction. The two instructions are not incongruous or contradictory. The term “instrumental” is defined by the court to mean such contribution by the plaintiff as that, without it, the sale would not have been made. In other words, the plaintiff must have been the moving cause which produced the sale or the procuring cause of the sale. (Armstrong v. Wann, 29 Minn. 126, 12 N. W. 345, approved in Shober v. Blackford, 46 Mont. 194, 127 Pac. 329.) We think the jury could not have been misled, and that the *538evidence is sufficient to make out a case under the rule thus announced.
The judgment and order are affirmed.
Affirmed.
Mr. Chief Justice Brantly and Mr. Justice Sanner concur.