What is the test for interpretation of language in a commercial contract?

In Burritt v. Stone, supra, Lamont, J., with whom Haultain, C.J., concurred, is reported as follows at p. 386: "The rule appears to be that, where the language in which the parties have embodied their agreement is clear and susceptible of only one meaning, that meaning must be given to it, though it may not be that which the parties intended. But where the language used is capable of more than one meaning, the circumstances surrounding the contract and the course in dealing between the parties may be looked at to see in what sense the parties were using the words." (emphasis added)