In horology, a movement, also known as a caliber, is the mechanism of a clock or watch, as opposed to the case, which encloses and protects the movement, and the face, which displays the time. The term originated with mechanical timepieces, whose clockwork movements are made of many moving parts. It is less frequently applied to modern electronic or quartz timepieces, where the word module is often used instead.
In modern mass-produced clocks and watches, the same movement is often inserted into many different styles of case. When buying a quality pocketwatch from the mid-19th to the mid-20th century, for example, the customer would select movement and case individually. Mechanical movements get dirty and the lubricants dry up, so they must periodically be disassembled, cleaned, and lubricated. One source recommends servicing intervals of: 3–5 years for watches, 15–20 years for grandfather clocks, 10–15 years for wall or mantel clocks, 15–20 years for anniversary clocks, and 7 years for cuckoo clocks, with the longer intervals applying to antique timepieces.
A mechanical movement contains all the moving parts of a watch or clock except the hands, and in the case of pendulum clocks, the pendulum and driving weights. The movement is made of the following components:
Watch movements come in various shapes to fit different case styles, such as round, tonneau, rectangular, rectangular with cut corners, oval and baguette, and are measured in lignes, or in millimetres. Each specific watch movement is called a caliber. The movement parts are separated into two main categories: those belonging to the ébauches and those belonging to the assortments.
In watch movements the wheels and other moving parts are mounted between two plates, which are held a small distance apart with pillars to make a rigid framework for the movement. One of these plates, the front plate just behind the face, is always circular, or the same shape and dimensions as the movement. The back plate has various shapes: