Abstract: A drum rotation indicator enables a crane operator to sense rotation of a drum, and thereby determine linear movement of a cable, that has one end wound about the drum. This indicator has a cam, that rotates with the drum, and a cam follower, that translates rotation of the cam into linear movement. A readout plunger is located conveniently for the operator's hand, and linear motion that is induced by the cam follower is transferred to the readout plunger by a medium that can be a mechanical linkage, a push-pull cable, or a hydraulic system. In a preferred embodiment of the invention, the cam follower disengages automatically from the cam after linear motion has been transferred to the readout plunger. The linear motion transferring medium also transfers motion from the readout plunger to the cam follower, which pivots into engagement with the cam. The cam has a serrated periphery, to give an instantaneous response, upon rotation of the drum, to engagement of the cam follower with the cam.