In calculating the amount of assessments to be charged against the respective tracts of land included in the annual district assessment roll, the per acre charge against the lands in class No. 1 on the base map shall be taken as one hundred percent and the per acre charge against the lands in other classes shall be reckoned on their respective final per acre percentages of the per acre assessment against the lands in said class No. 1.
RCW 86.09.475