Systems for measuring movement size and thickness
Great question but I can only give you a partial explanation of the movement descriptions for these shaped calibres. There were industry conventions to describe movement sizes and we are all familiar with the ligne of 2.256mm used to indicate the width of a movement. Another system was also used to express thickness, based on 1/12th ligne (douzième), ie, a thickness of 15/12 lignes is 2.82mm. Looking through V&C's photo archives, I see this method of recording movement thickness appeared from 1910 to 1920.
Yet another system was used to account for movements which have the size of back plate different from the front plate. This was also expressed as two numbers but not using a base of "12". Below you can see "Savonette" pocket watches with back plate measuring 20''' and front plate of 22 lignes width, etc.
Unfortunately, applying this system to the movement you are referring to would give an unrealistic result for a wrist watch. On this page, you can also see a bracelet watch from 1913 with movement described as 9 - 19/19. I can only speculate this is still a measure of thickness but following another convention. I would greatly appreciate if anyone can shed some light on this!
The World of Vacheron Constantin Geneve