I've been monitoring my Ananta closely for accuracy, as I do all my watches. I check every new watch against time.gov at least twice a day, often times as many as 4 times per day, and note the accuracy, including resting positions, daily activities and so on, when anomalies merit such notes.
Now, my Ananta is usually incredible accurate, presuming ideal conditions: i.e., if it's worn for a normal daily period and sleeps dial up/down, it will hit about +0.5/day. It fairs much worse crown up, losing about 3 seconds overnight, assuming it's roughly fully wound before sleep.
Now, I've noticed that as the mainspring unwinds to about 66%, it begins to slow down. It'll lose a couple seconds even in dial up position, eventually getting as bad as losing about 4 seconds a day assuming it never gets wound up past half way. (Obviously, this is a fairly contrived setup, as most people wearing their watch would have it wound quite high by day's end, but hey, this is science)
Well, I wear it so often that I don't let it wind down to the last 25% or so, but I did this time. It was about -6 about 24 hours ago, but was at about +/-0 when I checked it recently. So it had gained about 6 seconds in a day's time, crown up, near the end of its power reserve. I didn't want it to die, so I wound it half way after measuring.
So what are the results? Fully wound, it runs ever so slightly fast. Half wound it runs a little slow, but not badly. Nearly unwound it runs somewhat fast.
Quite a strange result and counter intuitive. Watch movement experts, why is this so?