Joe Grand has released his POV watch as an open source hardware project, nice!

The Persistence of Vision (POV) Watch takes advantage of the theory of persistence of vision to create a unique wristwatch that displays the current or elapsed time while the arm is swinging (such as during a run or brisk walk). A sequence of LED patterns from the watch are displayed in quick succession and interpreted by the wearer as a single, static image appearing in “thin air.”

A Microchip PIC16LF628A handles the image display functions and interfaces with a mercury switch to detect the current direction of motion, which allows the image to be displayed twice per cycle (arm moving out and arm moving back).