Abstract: In a rotating drum type of digital clock, the minute drum is fixed to the drum shaft. A drive disc is carried on the shaft, freely rotatable thereon, adjacent to the minute drum. Sandwiched between them is a detent ring which is keyed to the drive disc, but which has limited axial freedom with respect to both the disc and the drum, being pressed toward the web of the drum by a spring. Convex detent bosses extending axially from the ring can engage with any of a plurality of recesses in the web of the minute drum. The drive disc is advanced each minute by the normal actuating mechanism, and drives the minute drum through the detent ring. A setting knob is engageable with the shaft, permitting rotation of the latter, and hence of the minute drum, for setting purposes. In setting, the bosses are forced out of the recesses, the ring retracting axially, so that the drum can be rotated with respect to the ring.