Perhaps I should add that back in 1970 when I managed the shop there were few battery operated watches around. There were some 500 watches and 150 clocks on display. Can you imagine the problems if I'd had to strip the window every morning, reset and wind all the watches and clocks and then redress the window? No way would I have had the time (geddit?) to do that AND as the day progressed they would start to show various times .... OK perhaps only by a couple of minutes but ......