I was wondering if anyone could explain what the difference is between a regular Breguet hairspring and the "Lossier inner terminal hairspring" I always thought it refers to the way it fastens to the staff, but I've never seen an explanation of it either.Did waltham only use these on wind indicator Vanguards? Thanks in advance...Ted Brown.

Hi Theodore,

There are not really 'differences' between Breguet and Lossier. It is more of an issue of association of the two. Brequet is most closely associated with the actual 'overcoil' itself of a hairspring while Lossier is more specifically the type of curve and/or termination style. A Breguet overcoil may have a Lossier curve and or another fairly common style known as a Phillips curve. Both these are more of a tweak or specific shape vs. pinning relationship of the actual overcoil itself. By pinning I'm referring to the termination or the actual placement of the hairspring stud at the very end of the hairspring.

Lossier was basically a mathematician and he perfected what's known as Lossier's Rules. These rules relate most generally to a relationship of points at which a hairspring is 'pinned' with regard to the pinning point's radial, positional relationship to the pinning point of the inner coil at the collet attachment. This "inner terminal" terminology is obviously referencing the most 'inner' coil of the haispring and it's associated termination point where it is attached to the collet that fits on the staff. Most of this mathematical theory is aimed the actual degrees of excursion, (amplitude), that a balance makes in both directions after passing through center. Of course, this is really about accuracy and something called isochronism. Simply put it's an effort or theory designed to ensure that a mechanical watch hopefully maintains it's accuracy as the mainspring powers down to lower levels wherein the obvious lower power levels would potentially be interpreted into a 'lesser' amplitude of the balance wheel. A lesser amplitude would be exhibited as an actual 'gain' in the time train since the balance is passing through center more frequently.

I wouldn't get too excited about all this as much of it is theory. Some holds true, some does not. Many a mathematician has been involved in the early design days of watches, but unfortunately there are many other factors 'in play' inside a mechanical watch, and many of these factors cannot simply be dealt with via mathematical calculations. One of the most variable influences inside a mechanical watch relates to the oil, oiling, etc., and math doesn't generally help out much with oil/oiling.

I don't know the answer to your question about how many models of Walthams actually fit into the "inner terminal" style of hairspring, but I can tell you that the hairsprings in 'many' watches fit into the category of having a Lossier curve, or they at least exhibit that they have been designed and pinned 'somewhat' pursuant to Lossier's Rules. Hope this helps a little.

Regards,
Gene

The Lossier Inner terminal argument to open up the first wrap to leave a little more space for the expression of the balance spring around the center arbor was indeed spltting hairs! Waltham's billboarding the Lossier spring on the winding wheels of some of their later model watches was sort of like saying "premuim" for rubber tires. Especially with watches that when you open them up to clean them look like an entrance to a coal mine! However, the same arguments were applied to the Breguet curves (which were much more important to true isochronism and position accuracies), as illustrated by the incredible Joseph Bulova School of Watchmaking Training manual . . .

Bulova better illustrates the effect of NOT having the Breguet Balance spring as below . . .

David has addressed what this is 'really' all about with "Waltham's billboarding the Lossier spring..."

It's about selling watches, and the fact that watch companies would put 'anything' on a winding wheel if they thought it would help sell more watches.

Thanks, Gene and Dave,I appreciate the explanation,something I always wondred about but had nobody to ask.I guess the other watch companys would have done the same thing to help their sales if it really was a valuable feature...Ted Brown.