This was my first thought - an aftermarket modification, but nicely finished. It doesn't look like a one-off hackjob, so if it were aftermarket, perhaps it was done to several watches for some unknown reason...but then there's the book entry. I have to assume the author did some research to confirm..? An archives extract on this serial might be very interesting.
Exactly! This approach seems too crude. Has any other manufacturer ever allowed a balance wheel to be directly influenced in this way?
Click to expand...