2 Answers

Breguet, and every other watchmaker then and now, knew that watches tend to run a little fast, or a little slow, depending on the position of the watch: Gravity tugs on the regulating components link (mostly the balance and balance spring) differently whether the watch is crown up (as it would be in a pocket; boîtes de montres wristwatches didn't exist 200 link years ago) or in some other position.

Unscrew that crown and pull it out and you'll quickly notice that there's no phantom date position for the Trekker 39 the no-date versions swap out the Miyota 9015 for a naturally date-free link 90S5. Ticking at 4 Hz and rocking 24 jewels the 90S5 has hacking hand-winding and a power reserve of up to 42 hours. It's a simple reliable movement that link should operate in a fuss-free manner and create minimal headaches when it comes time for link a service.