Compressometers measure average deformation and strain of concrete cylinders during compression testing for determination of modulus of elasticity. The instruments consist of two yokes, mounted around the specimen. The bottom one is rigidly attached, and the upper one is hinged at opposite points to permit pivoting. A fixed rod connects the yokes. Yokes are lightweight aluminum alloy; other parts are cadmium plated steel. A mechanical dial or digital indicator measures specimen deformation at the two opposite positions. Dial indicators have 0.2in (5.08mm) range and 0.0001in (.0025mm) divisions. Models are available with either mechanical dial or digital indicators to fit standard 4in (102mm) or 6in (152mm) concrete cylinders.