In article ,
Andy Wade writes:
Cheap clock radios are the only things I've seen that have used crude RC
oscillators to cover mains outages, and their timekeeping is utter crap
- 5 min error in half an hour!

The old brass timeswitches which used to be used on streetlamps
(complete with auto seasonal adjustment) used to continue on clockwork
for several hours during a power cut. On power restore, the synchronous
motor also rewound the clockwork spring. Damn impressive pieces of
mechanical engineering those things were.

There's one road near me which obviously still has timeswitches on the
lamps, but no evidence of the clockwork standby operation, judging by
how all the lights can occasionally go out of sync for a month or so
before someone corrects them.

--
Andrew Gabriel