holes. One of these holes is actually a slot in order to engage the gears properly and adjust their tension so that they do not hind. Two 1.5-V alkaline D cells are connected in parallel across the potentiometer. The number of teeth on the gear is selected to give slightly less than 10 turns for the full pen travel. In our case we chose a 60-tooth brass gear from an old scale exoansion kit from a Beckman IR-33 which we no longer use. This gi\,es us 9.3 turns for the full scale pen travel. The o u t ~ uof t the ~otentiometertranslates the . Den -~osition into an analogvol
