NavList:

I have a 6 year old Rotary mechanical (automatic wind) Chinese built watch (about $100 back then) with glass faces showing the internals a la an open H4.( I fanstasize it maybe an H4 while at sea) Harrison would probably have recognised most of the wirly, tick tock  bits except maybe the movement winder and the lack of bi-metalic parts .The Invar alloy, temperature and magnetic insensitive, would have amazed him no doubt and made  some of his inventions, such as bi-metallic strips, obsolete.

3 years ago, I did a mock "Longitude prize test", 4 weeks (didn't go to Jamaica, just coastal sailing in Cornwall).

If warn on the wrist 24/7 at sea, it lost on average 20 secs per day.If warn just a few hours and removed, tended to lose anything from 10- 50 secs per day. So presumably the constant wearing reduces variable  temperature and static positon effects and gives more constant winding?

Anyways, a graph drawn through the 20 secs per day lost, gave me predicted rate which gave me good accuracy  after 4 weeks, well under 2 minutes out.So I claim the prize please, Longitude Board! With inflation, that would be about £3million. please pay direct into my offsore account. !

My favourite quartz is my Citizen eco drive divers, virtually bullet proof. Generally good for +2 secs per month whatever I do with it, direct sun, sea or dropping.

The pictures are not to scale! Roughly similar size.

I also like to do "no clock" cel nav using lunars,bit like Slocum, using a towed log to get distance run between observations. I haven't written up my recent few experiments yet, but Longitude by lunars and no clock generally within 30 nm. most of my longitudes using the Rotary were within 5-20 nm. So the clock beats the moon, at least with my lunars at sea.

All great fun! Greg, I think JS  Letcher used only an 8 day aircraft panel clock in the 1960s, $22 ($170 now).

Francis