Standard log rule. The international log rule, based upon 1/4 inch saw kerf, as expressed in the formula (D2 x 0.22)—0.71 D) x 0.904762 for 4 foot sections (D represents top diameter of log in inches; taper allowance, 1/2 inch per 4 feet lineal), is hereby adopted as the standard log rule for determining the board foot content of saw logs and, unless some other log rule or other method of measurement is agreed upon, all contracts hereafter entered into for the purchase and sale of saw logs shall be deemed to be made on the basis of such standard rule.