The cam is a mechanically shaped-profile component that transforms rotary motion into controlled translatory motion. In watchmaking, it is one of the most versatile devices: I find it in chronographs, calendars, special escapements, automatons and even in fluid display systems. It is not a recent invention: Charles Victor Adolphe Nicole employed it as early as 1844 for the chronograph reset mechanism, and the principle has remained unchanged since then.
In mechanical chronographs the cam appears in two distinct roles. The first is the heart cam, the heart-shaped cam mounted on the arbor of each chronograph wheel — seconds, minutes, hours. Its asymmetrical shape ensures that the reset lever, regardless of the hand position, always finds the shortest path to return it to zero. The second role is that of control: the cam-actuated or cam and lever system operates start, stop and reset via an oblong cam that moves overlapping levers. It is the architecture of the Valjoux 7750 and its direct derivatives, Sellita SW500 and BR-CAL.326 included. The column wheel — column wheel — solves the same problem with a tooth profile that offers smoother travel and more refined finishing, but requires more precise machining and higher costs. It is incorrect to say that one is absolutely better than the other: the 7750 has demonstrated in forty years of series production that the cam is as reliable as a column wheel, provided tolerances are respected.
In calendars the cam governs the jump of dates and months. The snail cam accumulates energy during the rotation of the minutes wheel and releases it in an instant to make the hours hand jump without bounce. In the classic perpetual calendar a 48-month cam — one rotation every four years — automatically manages common and leap years. Some manufacturers, as in the ProSet system, have eliminated the traditional cam by replacing the grand lever with retractable fingers; others, as in the Segreto di Lario, multiply the cams to divide the power reserve indication into two separate kinematic chains.
There are then less common uses. The hacking by snail cam of Romain Gauthier stops the balance wheel upon crown extraction and gives it back an impulse upon closure. The Reuleaux triangle used by Dann Phimphrachanh in the Seconde Vive is a three-sided curved cam that governs a seconds escapement. The oval cams of the Patek Philippe Celestial 6105G reproduce the seasonal variation of daylight. In the HYT 501-CM caliber a thirteen-position cam synchronizes the fluid hour indication with the analogic minutes indication. From the bench I have seen many movements returned for repair with the heart cam deformed by forced reset: it is the most frequent damage on poorly used vintage chronographs.