Location: Zurich, Switzerland
Date: September 29, 1995
During our timing course from October 23, 1995 until November 10, 1995 at the watchmaking school in Solothurn, we were confronted with one of the most complex device, the regulating organ.
I can’t and won’t illustrate the vast theoretical applications in horology neither developing the details of each of them - I would blast my scope. However, the two theoretical approaches from Caspari and Grossman may be synonym to all efforts put into this field of research. Both theories are about achieving isochronism of the oscillations of the regulating organ. Remember, chief factors that impair isochronism in the sprung balance are: the escapement, faulty poising of the balance and its spring, the play of the balance-spring between the curb-pins, centrifugal force, magnetic fields, etc.
Prior to start the timing course in Solothurn, a watchmaker apprentice needs to get himself ready! The correct tools need to accompany him... so let’s start with some tweezers which will help him to take off the pins, to prepare the Breguet end curve and to correct the position of the balance spring.
The Caspari rule, named after the man who discovered it, is an important theory in watchmaking. According to this rule, the angle between the starting point on the collet and the stud must be 90° or 270°, in order to retain the isochronism, the regular to-and-from motion of the balance wheel.
In other terms, the starting point of the balance spring on the collet should be linear with the center of the balance-staff and the curb-pins.
Jules Grossmann, 1829 - 1907, was a German horologist who spent most of his life in Le Locle where he was head of the School of Horology. Highly skilled in theory as well as practice, he formulated the scientific theory of timing. Author of «Horlogerie théorique» (Bienne and Paris 1912). He invented the inner terminal of the balance spring and evolved the theory of the pinning-point.
In order to enhance isochronism of flat balance-springs, the starting point of the balance spring in the main wearing position of a timepiece should always be pinned upwards.
Thanks to geniuses like Caspari and Grossman (and of course all other important watchmakers from the past), we have an important and wonderful database and know-how! I’m still intrigued that most of our actual knowledge is based on research and formulas which found their roots centuries ago..! Incredible don’t you think?