When a consideration is executory, it is not indispensable that the contract should specify its amount or the means of ascertaining it. It may be left to the decision of a third person or regulated by any specific standard.

Source: CivC 1877, § 911; CL 1887, § 3535; RCivC 1903, § 1229; RC 1919, § 844; SDC 1939, § 10.0508.