To decrement

To decrement means to decrease a quantity in successive steps of constant value, as opposed to Increment. In horology, the term applies to any display or counting device progressing through discontinuous jumps rather than continuous movement: a countdown decrements the seconds or minutes one by one, and the repeating mechanism of a striking watch decrements the number of strikes remaining to be Stamping as they are executed. The decrement corresponds to the value subtracted at each step; when it equals one unit, it is called a unit decrement. In a Movement mechanical, this step-by-step progression is achieved by components such as a rack falling onto a Snail (cam) or a step cam, a Finger training or a Neck chain (sautoir), which only allow the jump when crossing a notch and guarantee strictly equal intervals. The notion is central to jump-display complications, such as the Date / Calendar or jumping hours, and to devices for Counting repetitions and chronographs. It contrasts with continuous variation, characteristic for example of the movement of a trailing Hand or of a smoothly rotating Disc.