Longines 431 from 1968/69.
33600 vph ultrachron
I know it's an automatic but I want to get a sense of how worn my mainspring is.
I have hand wound it before (maybe 10-15 turns?). I *think* it started getting a little tight but it could just be me not wanting to break anything.
Maybe I should just buy a winder. Thoughts?
Follow-up question: When fully wound, how much reserve power did the 431 movement have new?