The 461891 is a contact tachometer. Surface wheels measure the contact surface speeds (10 to 9,999 rpm) of rotating objects. The memory button saves the last reading and recalls the min/max readings display. Complete with wheels for measuring linear surface speed (0.2 to 6560 feet/minute; 0.05 to 1999.9 meters/minute) or RPM. The kit includes a cone tip, flat tip, and spare wheel for measuring surface speed, as well as four AA batteries, a carrying box, and a user handbook.