Thank you very much.
I was looking at the relationship between the location of the pin on the caseback and the swing of the bumper.
So now I know what the curved slot in the bumper is for.
Similar location to the Vulcain 120. Also a twin barrel, but handwind, of course.
I am still trying to understand my Vulcain 401 movement, as this only has a single barrel, yet maintains reserve after the alarm is triggered. It must be two-stage, but how? And I dare not tear down the watch...