Glossary of Terms: Watches, Watchmaking and Horology

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

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Regulator: - Part of the balance mechanism used to make fine timekeeping adjustments. The regulator usually has 2 vertical pins which straddle the hairspring and can be adjusted to make the effective length of the spring longer or shorter, resulting in changes to the rate of the watch.
Repeater: - A device that chimes the time when the wearer pushes a button. Some repeaters, called "quarter repeaters" sound just the hours and the quarter hours ( by means of two different pitched tones); others called "five minute repeaters", sound the hours, quarters, and five minute periods after the quarter; and still others called "minute repeaters", sound the hours, quarters and minutes. See also "Minute Repeater."
Roller Jewel: - The jewel-pin that serves as the point of contact between the time-train and the balance wheel. Also called the impulse jewel. Also see our page on the use of jewels in vintage watches.
Rotor: - The part of an automatic (or self-winding) mechanical watch that winds the movement's mainspring. It is a flat piece of metal, usually shaped like a semicircle, that swivels on a pivot with the motion of the wearer's arm.
Safety Roller: - A small disc attached to the balance, with a crescent cut-out, which interacts with the guard-pin to ensure proper action of the escapement. The second roller in a "double-roller" watch.
Set-lever or Setting-lever: - The detent which engages a slot in the stem and pushes down the clutch lever. On a lever-set watch, the lever that is pulled out to place the watch in setting position.
Shake or Side-shake: - The horizontal freedom of motion of an arbor in its bearings. Also refers to the distance the escape wheel can be moved backward before the back of a tooth contacts a pallet jewel when the opposite jewel is at the moment of unlocking.
Single-roller: - A disc attached to the balance which contains both the impulse jewel and the safety crescent. Fell out of favor with the advancement of the double-roller.
Snap Back: - A case whose back "snaps" or "pops" off. Can also refer to the response you get from your watchmaker when you ask for the 12th time if your watch is done yet.
Staff: - The pivoted "axle" of a wheel, usually the balance wheel, as in "balance staff".
Stem (or winding-stem): - The shaft that connects the crown to the movement. Used to wind the watch and set the hands. The part that breaks when you force open a swing-out case without pulling out the crown.
Sterling Silver: - A precious metal. Sterling refers to silver that contains 92.5% silver 7.5% copper. This proportion is defined and fixed by law. The silver fineness should be stamped on the metal, sometimes accompanied by the initials of a designer or country of origin as a hallmark.
Strap: - A watchband made of cloth, rubber, leather or other non-metal material.
Stopwork: - A mechanism on the barrel of a watch or clock that permits only the "middle" portion of the mainspring to be used, thus utilizing that portion of the spring whose power is more even. Sometimes called a "Maltese Cross" or "Geneva Stopworks".
Sunk Seconds: - The small seconds dial which is depressed or "sunk" into the dial to prevent the second hand from interfering with the other hands.
Tank Watch: - A rectangular watch originally designed by Louis Cartier. The bars along the sides of the watch were inspired by the tracks of tanks used in World War I.
Tonneau Watch: - A watch shaped like a barrel, with two convex sides and two parallel sides.
Tourbillon: : - A complication designed to eliminate or substantially reduce positional timing errors due to the effects of gravity or unbalanced friction. The invention consists of mounting the entire escapement on a platform or mobile carriage which rotates on its axis within a given time period. Since any positional errors are reproduced at regular intervals, they tend to cancel each other out.
Train (see also Gear Train): - The interconnected system of gears and pinions which transmits power from the mainspring to the escapement. Does not refer to the engraving of a locomotive on your watch case.
UTC: - Universal Time Coordinated. A universal time based on the Greenwich Meridian used by the military and in aviation. Greenwich Mean Time (GMT) can be considered approximately equivalent to Universal Time Coordinated (UTC). GMT as such is now obsolete however, being replaced by UTC. Using this time zone/standard avoids errors and problems associated with different time zones and summer times operational in different countries.