by david pierce » Sun Aug 31, 2014 7:25 am
Jan,
The "experts" who write watch repair books are really no different than the rest of us. They get their information from various sources such as books wirtten by other experts, articles, interviews and practical experience. A lot of times when a number is thrown out to the rest of us it may be nothing more than an estimated guess. If one source says 1/3 and another source says 1/2 it does not mean that one is wrong and the other is correct. One number will simply run the mechanism longer than the other number.
That said, I feel that the smaller the watch, the more critical the issue of wasted space becomes. Larger watches and particularly clocks can afford a wider latitude in this area. In the end result the way the mechanism behaves determines the correct ratio of coil thickness to barrel space. Since the inversely proportionly control parameter controls the length of the spring, as the number gets larger you simply end up with a shorter spring and more barrel space. The margin of error is then the length of time the mechanism will run between windings.
david