"These instructions are to be followed throughout the Southern Region to establish uniform practices in regard to the measurement of land areas in performance work and subject to such revision, if any, as may hereafter be necessary, are applicable to the 1942 and succeeding program years. It is not the purpose of these instructions to give detailed procedures for classifying crops or entering data on the current performance reports for each farm, but rather to deal with problems in measuring fields and plots on a farm."