So one of my repairs this week was a vintage Waltham pocket watch. When I received the watch the balance pivots were badly damaged, the regulator pins were pinched against the hairspring, and the regulator had been moved all the way to one side.
As I disassembled the watch I followed my usual protocol, fixing problems as I find them. First thing I did was replace the balance staff which meant having to tighten the hub on the balance arm as well. Then I proceeded to poise the balance, only to find it very, very out of poise. Since the watch had timing washers all over the place I started there. I removed one 2 minute washer and the watch miraculously fell into perfect poise. Next, I opened up the regulator pins, straightened them and centered the hairspring between them. I put the watch in beat, centered the regulator arm on the balance cock and voila, the watch was running within a few seconds a day with a total delta of positions less than 10 seconds. It may not be perfect, but for a 90 year old watch, that seems pretty good to me.
The thing is, I did all that without having any before timing results to work with. I just followed the theory, corrected the obvious problems and the watch was telling time good again. <-- ok I got a little lucky probably, but I can't imagine what the delta would have been if I had left the 2 minute timing washer on the balance and the hairspring pinched tightly between the pins. This whole operation worked for two reasons. 1st, the theory works. 2nd, when Waltham made this watch they paid attention to the theory. The watch was designed and adjusted at the factory to run well, so it can be brought back to that condition without too much work. If the watch had been unadjusted originally it may have taken a lot more work including adjusting pinning points on the balance and all kinds of difficult things to get it to work. I'm glad they put the correct effort into the watch originally.