42. Effect of antecedent written agreement.

42.     Effect of antecedent written agreement.

If there is a previous written agreement which is unambiguous, the disputed instrument will be re-formed in accordance with it, and, if the agreement is ambiguous, oral evidence may be used to explain it according to the ordinary rules applicable in cases of ambiguity1. Where the original agreement is of doubtful construction and the conveyance is definite and unequivocal, it is not easy to avoid the conclusion that the conveyance may be the best evidence of the actual agreement between the parties2. If the previous written agreement is clear