alarm: A device that sounds a signal at a pre-set time

altimeter: A device that determines altitude by responding to changes in barometric pressure

anadigi display: A display that shows the time both by means of hour and minute hands (an analog display) and by numbers (a digital display)

analog display: A display that shows the time by means of hands and a dial

auto repeat countdown timer: A countdown timer (see "countdown timer") that resets itself as soon as the pre-set time has elapsed and starts the countdown again. It repeats the countdown continuously until the wearer pushes the stop button.

automatic winding: (also called "self-winding") Winding that occurs through the motion of the wearer's arm rather than through turning the winding stem. It works by means of a rotor that turns in response to motion, thereby winding up the watch's mainspring. An automatic watch that is not worn for a day or two will wind down and will need to be wound by hand to get it started again.

balance spring: A very fine spring (also called a "hair spring") in a mechanical watch that returns the balance wheel back to a neutral position

balance wheel: The part of a mechanical watch movement that oscillates, dividing time into equal segments

battery reserve indicator: See "power reserve indicator."

bezel: The ring, usually made of gold, gold plate or steel, that surrounds the watch face

bi-directional rotating bezel: A bezel that can be moved either clockwise or counterclockwise. These are used for mathematical calculations (see "slide rule") or for keeping track of elapsed time (see "elapsed time rotating bezel").

built-in illumination: Lighting on a watch dial that allows the wearer to read the time in the dark

calendar: A feature that shows the day of the month, and often the day of the week and the year. There are several types of calendar watches. Some show the date and day of the week with subdials and analog hands. Others have a scale on the outer rim of the watch face numbered from 1 to 31 for the days of the month. Still others show the day, date, and often the year digitally through an aperture on the watch face.

caliber. A watch movement

chronograph:A stopwatch, i.e., a timer that can be started and stopped to time an event. There are many variations on the chronograph. Some operate with a center seconds hand which keeps time on the watch's main dial. Others use subdials to time elapsed hours, minutes and seconds. Still others show elapsed time on a digital display on the watch face. When a chronograph is used in conjunction with specialized scales on the watch face it can perform many different functions, such as determining speed or distance (see "tachymeter" and "telemeter") Some chronographs can time more than one event at a time (see "flyback hand" and "split seconds hand"). Do not confuse the term "chronograph" with "chronometer." The latter refers to a timepiece, which may or may not have a chronograph function, that has met certain high standards of accuracy set by an official watch institute in Switzerland. Watches that include the chronograph function are themselves called "chronographs."

chronometer: A timepiece that has met certain high standards of accuracy set by an official watch institute in Switzerland. Do not confuse with "chronograph".

countdown timer: A function that lets the wearer keep track of how much of a pre-set period of time has elapsed. Some countdown timers sound a warning signal a few seconds before the time runs out-these are useful in events such as yacht races, where the sailor must maneuver the boat into position before the start of a race.

crown: Button on the outside of the watch case that is used to set the time and the calen- dar, and, in a mechanical watch, to wind the mainspring. In the latter instance, it is also called a "winding stem".

crystal: The transparent cover on a watch face made of glass crystal, synthetic sapphire or plastic

day/night indicator: A colored or shaded band on a world time dial (see "world time dial") that shows which time zones are in daylight and which in darkness

depth alarm: An alarm on a divers' watch that sounds when the wearer exceeds a pre-set depth. In most watches it stops sounding when the diver ascends above that depth.

depth sensor/depth meter: A device on a divers' watch that determines the wearer's depth by measuring water pressure. It shows the depth either by analog hands and a scale on the watch face or through a digital display

dial: The watch face

digital watch: A watch that shows the time through digits rather than through a dial and hands (analog) display

elapsed time rotating bezel: A graduated rotating bezel (see "rotating bezel") used to keep track of periods of time The bezel can be turned so the wearer can align the zero on the bezel with the watch's seconds or minutes hand. He can then read the elapsed time off the bezel. This saves him having to perform the subtraction that would be necessary if he used the watch's regular dial.

engine turning: Decorative engraving, usually on a watch face

escapement: Device in a mechanical movement that controls the rotation of the wheels and thus the motion of the hands

flyback hand: A seconds hand on a chronograph that can be used to time laps or to determine finishing times for several competitors in a race. The wearer starts the chronograph, putting both the flyback hand and the regular chronograph seconds hand in motion. To record a lap time or finishing time, he stops the flyback hand. After he takes the reading, he pushes a button and the hand will "fly back" to catch up with the constantly moving elapsed-time hand. He repeats the process to record as many lap times or finishing times as needed.

gear train: The system of gears which transmits power from the mainspring to the escapement

gold plated: Consisting of a layer of gold over base metal

grande sonnerie: ("GRAHND sohn er EE"): A type of repeater that sounds the hours and quarter hours when the wearer pushes a button.

guilloche: A type of engraving in which thin lines are interwoven, creating a patterned surface

index: An hour indicator on an analog watch dial, used instead of a numeral

quartz crystal:A tiny piece of synthetic quartz that oscillates at the rate of 32,768 times a second, dividing time into equal segments

quartz movement: A movement powered by a quartz crystal to vibrate

repeater: A device that chimes the time when the wearer pushes a button. Some repeaters, called "quarter repeaters" sound just the hours and 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

rotating bezel: A bezel (the ring surrounding the watch face) that can be turned. Different types of rotating bezels perform different timekeeping and mathematical functions (see "elapsed time rotating bezel," "unidirectional rotating bezel," "bidirectional rotating bezel" and "slide rule.")

rotor: The part of an automatic, or self-winding, 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.

sapphire crystal: A crystal (the cover that protects the watch face) made of synthetic sapphire, a transparent, shatter-resistant, scratch-resistant substance

screw-lock crown: A crown that can be screwed into the case to make the watch watertight

second time-zone indicator: An additional dial that can be set to the time in another time zone. It lets the wearer keep track of local time and the time in another country simultaneously.

shock resistance: As defined by U.S. government regulation, a watch's ability to withstand an impact equal to that of being dropped onto a wood floor from a height of 3 feet

skeleton case: A case with a transparent front or back that allows the wearer to view the watch's movement

slide rule: A device, consisting of logarithmic or other scales on the outer edge of the watch face, that can be used to do mathematical calculations. One of the scales is marked on a rotating bezel, which can be slid against the stationary scale to make the calculations. Some watches have slide rules that allow specific calculations,

tonneau watch: A watch shaped like a barrel. with two convex sides

totalizer: A mechanism that keeps track of elapsed time and displays it, usually on a subdial or subdials on the watch face. Same as a "recorder" or "register". The term "totalizer" can be used more generally to refer to any counter on a watch, such as a stroke counter on a golf watch, which lets the wearer keep track of his score by pushing a button after each stroke.

tourbillon: ("TUR bee ohn"): A device in a mechanical watch that eliminates timekeeping errors caused by the slight difference in the rates at which a watch runs in the horizontal and vertical positions. The tourbillon consists of a round carriage, or cage, holding the escapement and the balance. It rotates continuously at the rate of once per minute.

12-hour recorder (or register): A subdial on a chronograph (see chronograph) that can time periods of up to 12 hours

unidirectional rotating bezel: An elapsed time rotating bezel (see "elapsed time rotating bezel"), often found on divers' watches, that moves only in a counterclockwise direction. It is designed to prevent a diver who has unwittingly knocked the bezel off its original position from overestimating his remaining air supply. Because the bezel moves in only one direction, the diver can err only on the side of safety when timing his dive. Many divers' watches are ratcheted, so that they lock into place for greater safety.

water resistance: The ability to withstand splashes of water. Terms such as "water resistant to 50 meters" or "water resistant to 200 meters" indicate that the watch can be worn underwater to various depths.

winding stem: The button on the right side of the watch case used to wind the mainspring. Also called a "crown."