Left: A "warning"9 occurs sometime before the unit wheel reaches 0.This is the step where arm B leaves the ratchet wheel R, the arm C having already come in reach of R. The spring S then pushes R so that a tooth hits the upper arm C. This is a safety measure ensuring that only one digit is added. Notice that when arm B leaves the wheel R, this wheel has some recoil and the position of the spring S has to take this into account. However, this recoil is greatly decreased by a mobile part at the end of arm B. (This mobile part cannot turn in the second phase.) When the unit finally has to be added, arm B again enters the teeth of R, forces R to turn, and forces the spring S to go over one tooth, which it wouldn't have done by itself. Right: The mechanism immediately after carrying. Arm B has entered a tooth and forced R to turn by one tooth, that is one unit. The spring S is positioned in such a way that R will rotate counterclockwise when arm B leaves R.