Ratchet wheel 1 rotates about fixed axis B. Lever 2 is a pawl having two teeth, a and b, and turns about fixed axis A. Lever 4 with notches c turns about fixed axis C. When ratchet wheel 1 turns clockwise, tooth a of lever 2, held against the wheel by spring 3, enters a tooth space of the ratchet wheel. Lever 2 turns counterclockwise about axis A and tooth b enters a notch c on oscillating lever 4 and stops the lever. Upon further rotation of ratchet wheel 1, tooth a is pushed outward by the next tooth on wheel 1, and tooth b is withdrawn from the notch on lever 4 thereby releasing the lever.
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