Speedmaster chrono hand jumps forward

Although many people believe magnetism only affects timekeeping, it has other undesirable effects also.

I made this video to show another fault (lack of the "stem bolt for hammer" part) but what it does show quite well is that when the chronograph is started, the hammer that resets both the seconds counting wheel and minutes counting wheel lifts off the cams of both of those wheels. The hammer is the part you see moving there that has an inverted Y shape...sort of:


When the hammer lifts off the cam, there is a brief moment where the chronograph seconds recording wheel is free, just before the coupling yoke comes in to make contact with it and starts to make it turn. If the hammer is magnetized (or has too much oil, or the oil is sticky) then it can cause the cam on the wheel to stick to the hammer, and this will make the wheel move slightly just before it starts to be driven - as the hammer moves away it wants to take the cam with it, and this causes rotation of the wheel and movement of the hand.

So although some watchmakers say they almost never use their demagnetizers, this is yet another reason why every watch being serviced should be demagnetized, and why watch owners will often buy themselves a demagnetizer. There are more magnetic fields around us than ever before, so sources of magnetism are all around us.

Cheers, Al