Doc has inspired me with this in-depth and surprising examination of different aspects of V&C timepieces. In that spirit I'd like to present this vignette .
One interesting aspect of V&C chronometery is the evolution of the micro-adjusting fine regulator. For comparison, I have two Observatory watches seperated by 15 years. Both obtained a 3rd Prize at the Geneva Observatory so lets assume they fairly represent the evolution of timekeeping over the interval.
In 1912, this swan-neck fine regulator was paired with a revolutionary balance wheel which was characterized by its split bimetallic anibal-brass composition. Dr. Guillaume referred to this device as his Balancier Integral/Integral Balance until a 1920 Nobel Prize affixed his surname by popular useage.
In 1922, Vacheron & Constantin registered Swiss Brevet (Patent) #101652 under the classification of Raquetterie de montre, or fine adjustment of watch. The actual patent was granted a year later, in November of 1923.
Enter this 1927 Observatory movement, still featuring Dr. Guillaume's wonderful balance and also the new micrometer regulator. Two features allowed for greater precision of adjustment; an eccentric screw to move the regulator in the smallest of increments combined with a vernier scale engraved onto the regulator. Notice how the two sides do not align in every position; this allowed for more precise indication of the setting.