"Synonym of size. Sully used this term circa 1715 to denote the layout and dimensions of the different movement pillars, wheels, barrel, etc. Since then "calibre" has been used to indicate the shape of the movement, its bridges, the origin of the watch, its maker's name, etc.
The round calibre is the most commonly encountered. It is described in terms of its casing diameter, measured in lignes or millimetres, for example a 10''' / 22.5 mm round calibre. The shape and layout of the bridges is used to distinguish between a bridge calibre, in which each part of the train has a bridge, the revolver calibre, whose barrel bridge bears a slight resemblance to a pistol, the curved bridge calibre, where the bridges curve towards the centre of the movement, and the three-quarter-plate calibre in which the entire train except for the escape-wheel is fitted under a bridge that covers some three-quarters of the movement." (FHH)
The movement is the mechanism inside of a watch case that drives the hands and other complications. A specific calibre is the reference for a particular movement.
An Ebauche, "An incomplete watch-movement. Until about 1850, the ébauche consisted only of the bottom plate, bars, fusee and barrel. The old Genevese watchmakers called the ébauche le blanc, i. e. the blank.
In the early 19th century, the ébauche was made up of two plates with pillars and bars, the barrel, fusee, index, click and ratchet-wheel, and a few assembling-screws. These parts were all roughly filed and milled. The steel and brass parts were manufactured in special workshops. The ébauche was finished in the finishing-shop (comptoir d'établissage).The modern ébauche is a jewelled or non-jewelled watch-movement, without its regulating organs, mainspring, dial or hands." (Berner)