A bi-directional, one-digit, base-10 mechanical counter. It is designed such that strings should be attached to the 'ratchet pulling arms' , and a rubber-band should connect both ratchet pulling arms to one another, looping around an m3 bolt protruding from the zero_detect_frame block.
Print out 1 copy of all of the pieces, and two copies of the ratchet_pulling_arms. 693 bearings are used in the string_pulley and in the zero_detect_arm. 623 bearings are used in the ratchet_gear and the front of the zero_detect_arm (the bearing that rolls along the counter wheel). A spring (or rubber band) should be stretched from the hook hanging down from the zero_detect_arm to the same screw the rubber band connecting the pulling arms is wrapped around. A 1/4" diameter spring, about .3" long is used to force the ratchet_detent_arm into place. Liberally apply M3 nuts and bolts to secure everything.
You should be able to increment and decrement the counter by pulling on either one of the strings.