File:Mainspring torque curves.svg

English: Graph of torque exerted by two pocketwatch mainsprings enclosed in mainspring barrels as they unwind. Traced from graph originally from 1879 watchmaking book by Claudius Saunier. The vertical scale units were labelled as 'pounds' in the text although they represent torque. The horizontal units are revolutions of the mainspring barrel, from fully wound at left. The curves illustrate the benefit of the going barrel in providing more constant torque to the watch's movement, improving timekeeping. The torque of a free mainspring outside a barrel declines in a straight line to zero as it unwinds. The effect of the enclosing barrel, seen especially in the lower curve, is to create a 'flattened' section in the torque curve, providing roughly constant torque to the watch's gears over the running time of the watch, until the spring is nearly unwound. Alterations to image: Traced curves from original image of graph, horizontally reversed curves to place fully wound side on left.