Interlox Master Slide rule, made of wood and featuring 12 segments that extend out to full length, then slide back together for storage. The connectors are steel, and the segments are printed in black and red. Depending on which side you use, the slide rule is marked "Inside measure" or "Outside measure." Made by the MasterRule Mfg. Co. Inc. of New York, the maximum length is 72 inches (6 feet) when fully extended. Closed, it measures 8 x 2.25 x 1/2 inches.