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As with many other Waltham watches, the Model 92 movement utilizes a Breguet hairspring which allows it to be adjusted for isochronism and a bi-metallic split balance wheel which compensates for changes in temperature . Initially, the hairspring stud, the means by which the hairspring is attached to the balance bridge, is round which is typical of that used by Waltham and many other manufacturers. It is worthy of mention, however, because it will change with run 10517801-10518500. At that point the patented Waltham stud is introduced. The patented stud allows the balance wheel and hairspring assembly to be detached and reattached to the balance bridge while these components are in the watch, thus avoiding stressing or bending the hairspring. The photo below, from Waltham’s “Watchmaker’s Handbook”, shows the patented stud after being released.
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The Model 92 Story > Movement Variations >