From Spanking Art

The spankometer is an electronic gadget (45 (W) x 65(D) x 30 (H) mm) that works similar to a pedometer. While a pedometer counts steps, the spankometer, which comes with a wrist strap, keeps track of the number of strokes and the time taken.

Apparently the gadget was widely (mis-?)understood to be a masturbation monitor (from the phrase "spanking one's monkey"). Possibly it can be used for both purposes.

The gadget used to be available at (in 2006?) but as of 2009 it's no longer there to be found.