Fixing Beat Error - Breaks positional accuracy? Why?

[everydaymastery]

Greetings,

I have just obtained an older 7750 chronograph that's in great shape and running well. It was +8s/d after a week on the wrist, and I checked it on the timegrapher. The first thing I noticed was that the beat error was around 0.5ms - 0.8ms in various directions. Dial down was around +10, and crown up was +6. I took a lot of measurements before changing anything on the hairspring.

I thought fixing the beat error was the first thing to do - so I got it down to under 0.2 and noticed something frightening: It would now gain 30+s/d in one direction, and lose 10s/d in another. Wild positional in-accuracy! I then moved it back to a 0.5 to 0.8 and regulated the movement down to -2 Dial Down / +2 Crown Up. After a few MORE days on the wrist it seems to be stable and keeping great time.

Why is this happening?!
Thanks!
- Kris

[rogart63]

No idea. Maybe the hairspring is touching something if you lower the beat error?  But i wouldn't sweat to much if the beat error is 0,5. As long as the watch is accurate.