All sections have square ends. Every joint opens on even number. Inside marked with 6 scales in a 16 in module. Scales are as follows: two courses in 16 in space (for concrete blocks and glass blocks). Three courses in 16 in space (for facing tile). Four courses in 16 in space (for Roan brick). Scales include mortar space and spacing for 6 in and 12 in blocks. Outside is graduated on both edges to 1/16ths. First end section is a short section which permits butting the rule on the first 16 in module.