from purely mechanical to quartz and some companies made very accurate ones. They were just beginning to get really good control of the balance wheel oscillations when quartz came along and killed the technology dead :<(
Definitely interesting collector pieces and you have restored one to almost factory appearance!
Great job and I hope the battery revives it :>) I don't know if this model has the balance swinging at 18,000bph or higher but some of them went as high as 36,000bph and had sweepers as smooth as the GS.