Glossary of Terms: Watches, Watchmaking and Horology

Glossaries are listed alphabetically. Click on the letter-index below.

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Cabochon: - Used to indicate a smooth round or oval convex shaped polished gemstone. In watch terminology, it often describes a decorative stone set in the watch crown.
Calendar: - The calendar mechanism on a watch can consist of a date only showing in a window to a triple calendar, showing the date, day and month. The most complicated calendar mechanisms may be mechanically driven to show the year and months including those with less that 31 days; leap years can also be mechanically allowed for. Sometimes referred to as a perpetual calendar mechanism.
Caliber / Calibre: - A word used to denote a unique movement model or design. Used for both quartz and mechanical movements. Also called Grade on American watches.
Cannon Pinion: - A thin steel tube with pinion leaves at its lower end and which carries the minute hand on its upper end. Provides a friction "clutch" with the center arbor when setting the watch.
Case or Watchcase: - The metal housing that contains the internal parts of a watch. Can be made of almost any metal. Many vintage pocket watch cases are brass or base-metal plated with gold. There were also many alloys of nickel used for pocket watch cases. For wristwatches, stainless steel is the most typical metal used, but titanium, gold, silver and platinum can also be used.
Caseback: - The portion of the case covering the back of the watch.
Chronograph: - Not to be confused with Chronometer. Originally "time-writer". A chronograph is a fully-functional watch, with the addition of a start-stop timer. Most chronographs are operated by two "pushers," one to start and stop the chronograph second hand, and the other to return that hand to the starting position..
Chronometer: - This term refers to a precision watch that is tested in various temperatures and positions, thus meeting the accuracy standards set by C.O.S.C. in Switzerland. These watches are provided with a chronometer certificate detailing specific test results by the C.O.S.C.
Clepsydra -: Also known as a "water clock", an ancient Greek time-keeping device similar to an hour-glass, which used a regulated flow of water or mercury through a small aperture to mark the passage of time. It is said that the clepsydra was invented to limit the speaking time of Greek orators (public speakers), which means that the first clocks were really invented for the purpose of encouraging politicians to sit down and shut up!
Click: - The pawl which prevents the ratchet wheel from turning backward when the mainspring is wound.
Clutch or Clutch Wheel: - A cylindrical winding part, with beveled ratchet teeth on its upper end, a groove in the middle, and teeth on its lower end. Slides back and forth as the watch is moved from winding to setting position. Also called castle wheel.
Cock: - A complementary part fixed to the main plate to form the frame of a watch movement. A cantilevered bridge which is supported at only one end. An overhanging support for a bearing or jewel e.g. the balance cock.
Coin Silver: - An alloy of 90% fine silver and 10% copper. It is called coin silver because early US coins were a ready source of this raw material and were sometimes melted down and made into watch cases.
Compensating Balance: - A bimetallic balance often constructed from brass and steel, and split near the balance arms and constructed so that its effective diameter will contract or expand with changes in temperature.
C.O.S.C.: - Control Officile Suisse de Chronometers or Swiss Controle Officiel des Cronometres- the independent Swiss regulatory organization that rigorously tests and certifies (or fails) watch movements for chronometer status.
Crown: - The knob used to wind the watch and set the hands.
Crystal: - The glass piece (or clear plastic) that protects the dial and hands. The probability of breaking the crystal is directly proportional to the difficulty and expense of finding a replacement.
Curb Pins: - The two regulator pins which "pinch" the balance spring and govern the fine-timekeeping of the watch by effectively changing the length of the balance spring
Cuvette: - The inner cover on the back of a watch case. Typically found on hunter-case watches.
Dennison Gauge: - Aaron Dennison was one of the "Fathers" of the American watch industry, and he invented several standards of measuring watches and mainsprings. The Dennison Gauge for watch sizes is based on a size A being 1" and for each additional size larger, you would add 1/16". The most common sizes were N (1 11/16), which is close to 18s and L (1 10/16), which is close to 16s. Used primarily by the E. Howard Watch Company (of which Dennison was a founder). Dennison Gauge is still used for the measurement of mainsprings for American pocket watches.
Detent: - The setting lever, or the part of the watch that retains the winding stem. Also refers to that part of a chronometer escapement that locks the escape wheel.
Dial: - The "face" of the watch. Most commonly made of metal, or glass-like porcelain enamel on a metal substrate. Can also be made from a wide variety of exotic materials and metals.
Double Roller: - Two discs mounted on the balance staff: a larger disc which holds the roller jewel, and beneath it a smaller crescented disc which, along with the guard pin on the pallet, provides the roller safety function.
Douzième: - One-twelth of a Ligne. A unit of measurement used for (usually) Swiss and French watches. Often used to state the thickness of the watch movement. One Ligne is 0.1879mm or 0.0074 inches. There are 12 douzième to one Ligne, 12 Ligne to one French inch (pouce, French for thumb) and 12 pouce to a French foot (Pied).
Draw: - The force which holds the pallet against the banking pins. Draw results from the combined angles of the escape wheel teeth and the pallet-jewel locking faces.
Drop: - The amount of the unrestrained motion of the escape wheel as it leaves one pallet jewel and drops onto the locking surface of the other pallet jewel.
Dynamic Poise: - Poising a balance by measuring its errors on a timing machine while the watch is running in different positions. Dynamic poise compensates for the motion of the entire oscillating balance system.