approximately 10 in. [255 mm] in diameter, with a center opening approximately 4 in. [100 mm] in diameter, made of nonabsorbing material not attacked by the cement, shall be used with the flow mold to prevent mortar from spilling on the table top. 5.2 A caliper consisting of one fixed jaw and one jaw movable along a permanent scale shall be provided for measuring the diameter of the mortar after it has been spread by the operation of the table. The scale shall be machine divided into 40 increments with 0.16 in. [4.0 mm] betweendivisions with major division lines every 5 divisions and the increment number every 10 divisions (Note 5). The construction and accuracy of the caliper shall be such that the distance between the jaws shall be 4 6 0.01 in. [100 6 0.25 mm] when the indicator is set at zero. NOTE 5—The caliper is graduated to indicate one fourth of the actual flow percentage, so that the readings of four measurements on the caliper may be added to give the flow value without the necessity of calculating the average of four individual measurements of the total flow.