Interesting quirk on my AP Diver

[kctt]

I've had the watch from new for 10 years now and found an interesting quirk that I never knew. These days, the watch is hardly worn and sits in the watch drawer.

Two days ago, I decided to set the time to the 10:10 position. At this time, the watch does not have any power reserve left. I don't remember the position of the hour and minute hands, just that I set it to 10:10. When I screwed the crown back on, I noticed the watch was ticking. I didn't move the watch that much to have caused the rotor to wind the watch. Hmmm... maybe the mainspring hasn't fully unwound I thought. Strange.

The next morning, the watch stopped running but the time showed 4 o'clock! Means the watch was actually ticking for 6 hours! I then set it to 10:10 again but this time was careful not to move the watch at all. Again, the watch was ticking after I screwed the crown. This morning, I found the watch showing around the half past 4 mark again! I repeated the exercise and this time watch stopped just before 5 o'clock. Seems like the watch runs for around 6 hours each time.

Before you guys say anything, I didn't wind the watch, it was on the set time position. What do you think happened here? I'm keen to hear if anyone came across this before.