[mark_in_manc]

Some of the IBM / ITR master clocks have that catch-up arrangement (mine does), and some don't. It's great fun when it's time to put the clocks back, as the thing clonks away for 11 hours worth of minutes to bring the slaves back to the right time. Perhaps it's worth noting that this is a different mechanism from that to pick up missed minutes every hour, which we have been discussing.

The mainspring on my master lasts for about an hour - it is wound by quite a clever eccentric on a 240v motor / gearbox combo, which operates a ratchet. Once the spring is wound, the ratchet 'misses', so the mainspring is not overwound.