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Old fashioned digital flip clocks display digits on flip-down leaves. The mechanisms are described in this page.

Summary

The earliest form of digital clock displayed the digits (and possibly days or the week and months), each split into top and bottom halves on adjacent leaves in a pack as in this animation. These are brought into Restart Parties from time to time as cherished legacy items, or treasured finds from a car boot sale or similar. They were electromechanical devices with ingenious mechanisms which it helps to understand in any repair situation.

Safety

Old mains powered devoces may have worn or perished insulation on the mains lead, creatng a shock or fire hazard. In the oldest devices, the design may be inerently insafe, for example with no earth connection to exposed metal parts.