The 461891 is a contact Tachometer. The contact surface speeds of rotating objects are measured by surface wheels (10 to 9,999 rpm). The memory button stores the most recent reading and displays the lowest and highest values. With wheels for measuring linear surface speed (0.2 to 6560 feet/minute; 0.05 to 1999.9 meters/minute) or revolutions per minute (RPM). It includes a cone tip, flat tip, and spare wheel for measuring surface speed, as well as four AA batteries, a carrying case, and an instruction booklet.