Calibre

Synonym of size. This term was used by Sully around 1715 to denote the layout and dimensions of the different parts of the movement, the pillars, wheels, barrel, and so forth. Since then the term has been used to refer, among other things, to the shape of the movement, its bridges, the origin of the watch or the name of its maker. Examples: the round calibre is the most frequent shape and the term refers to its casing diameter, measured in lines or millimetres: a 10'''/23.7 mm round calibre, for example. The shape and layout of the bridges are used to distinguish between a bridge calibre, in which each part of the train has a bridge, the revolver calibre, whose barrel bridge is vaguely reminiscent of 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 spanning some three-quarters of the movement.