In horology, a movement, also known as a caliber or calibre (British English), is the mechanism of a watch or timepiece, 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. The movement of a digital watch is more commonly known as a module.
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 a 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.
Mechanical movements
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:
;Power source: Either a mainspring, or a weight suspended from a cord wrapped around a pulley. A mechanism on the mainspring or pulley allows it to be wound up, with a ratchet to prevent unwinding. Gear teeth on the barrel or pulley drive the centre wheel.
;Wheel train: A wheel train is a gear train that transmits the force of the power source to the escapement. Large wheel gears mesh with smaller pinion gears.
The wheels in a typical going train consist of a centre wheel, third wheel, and fourth wheel. A separate set of wheels, the "motion work", divide the minute hand's motion by 12 to move the hour hand. Watches are fitted with an additional set known as the "keyless work", which enables the hands to be set.
;Escapement: An escapement is a mechanism that allows the wheel train to advance, or escape a fixed amount with each swing of the balance wheel or pendulum. It includes a gear known as the escape wheel, which is released one tooth at a time by a rocking lever. Each time the escape wheel moves forward it exerts force on the pendulum or balance wheel, pushing it to keep it in motion.
;Oscillator: The timekeeping element, either a pendulum or a balance wheel. It swings back and forth, with a consistent and precise time interval between each swing, called the beat. A pendulum movement has a pendulum hangar. This is usually attached to a sturdy support on the back, from which the pendulum is suspended and a fork which gives the pendulum impulses. The oscillator always includes the means to adjust the rate of the clock. Pendulums are usually fitted with an adjustment nut under the bob, while balance wheels have a regulator lever on the balance spring.
<span class="anchor" id="types"></span> Types of movements
thumb|upright=1.2|A modern bridge watch movement
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.
See also
- Clockwork
- Chinese standard movement
- Spring Drive