The Fluke 930 Tachometer and Fluke 931 Tachometer (the Tachometer) are handheld instruments that precisely measure rotational Rotations by Minutes (RPM). The Fluke 931 measures surface speed as well as length. Use red headlight function to do contactless RPM measurement. The Fluke 931 uses the mechanical adapter and selectable tip to make RPM measurement with contact. The Memory function allows you to store the last reading, as well as the maximum (Max), minimum (MIN), and medium (AV).