Roundness Measuring Machine's introduction-part 1 Roundness measuring instrument is a measuring tool for measuring the roundness error of workpieces by using the rotary axis method. The roundness tester is divided into two types: sensor rotary type and workbench rotary type. During measurement, the measured part and the precision shaft system are installed concentrically, and the precision shaft system is equipped with an inductive length sensor or a workbench for precise circular motion.