Acrylic Crystal - An acrylic crystal composed of plastic composite that is generally less expensive than a glass or mineral crystal. Sometimes called an "unbreakable" crystal, though this is a misnomer as they can definitely break. A high-quality acrylic crystal has optical properties very similar to glass.

Analemma - In astronomy, an analemma (Latin for the pedestal of a sundial) is a curve representing the angular offset of a celestial body (usually the Sun) from its mean position on the celestial sphere as viewed from another celestial body (usually the Earth). For instance, knowing that Earth's average solar day is exactly 24 hours (by definition), an analemma can be traced by plotting the position of the Sun as viewed from a fixed position on Earth at 24-hour intervals for an entire year. The resulting curve resembles a figure 8. This curve is commonly printed on globes. See also "Equation of Time."

Atomic Time Standard - Provided by the U.S. National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado. Atomic time is measured through vibrations of atoms in a metal isotope. The result is extremely accurate time that can be measured on instruments. A radio signal transmits this exact time throughout North America and some 'atomic' watches and clocks can receive them and correct to the exact time.

Automatic Winding (also called self-winding) - A mechanically powered watch that is wound by the motion of the wearer's arm rather than through turning the winding stem (manual mechanical). In response to this motion, a rotor turns and winds the watch's mainspring. If an automatic watch is not worn for a day or two, it will run down and need to be wound by hand to get it started again.

Balance Wheel - The spring-governed oscillating wheel that governs the timekeeping accuracy of the watch. This is the part of the watch that moves at a steady rate to measure the time.

Balance Staff - The arbor (or axle) for the balance wheel. The part that often breaks when you drop your watch.

Band - A generic term used to refer to the band that holds a watch on your wrist. The preferred terms are bracelet and strap, which more clearly describe the two major types.

Barrel - Also called "mainspring barrel." Thin cylindrical "can" which holds the mainspring of a watch. The toothed rim of the barrel drives the train, usually through the center wheel.

Bezel - Part of the case. The ring that holds the crystal in place.

Bow - Part of the case. The loop to which a watch strap or chain is affixed. The part that comes off, allowing your watch to fall to the floor when you're pulling it out of your pocket.

Bracelet - A bracelet is the flexible metal band consisting of assembled links, usually in the same style as the watchcase. Detachable links change the length of the bracelet. Bracelets can be made of stainless steel, sterling silver, gold, or a combination. See also strap.

Bridge - Complementary part fixed to the main plate to form the frame of a watch movement. The other parts of the watch are mounted inside the frame (part of the "ébauche").

Cabochon - Used to indicate a smooth round or oval convex shaped polished gemstone. In watch terminology, it 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.

Case or Watchcase - The metal housing that contains the internal parts of a watch. 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. A chronograph is a stopwatch. 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 certifcate detailing specific test results by the C.O.S.C.

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.

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.

Cuvette - The inner cover on the back of a watch case. Typically found on hunting-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.

Dial - The "face" of the watch. Most commonly made of metal, or glass-like fired vitreous enamel (sometimes incorrectly called porcelain).

Ebauche - A "raw" or unfinished movement.

Engine Turning - Decorative engraving, usually on a watch dial or case.

Equation of Time - The difference, over the course of a year, between time as read from a sundial and a clock. It can be ahead by as much as 16 min 33 s (around November 3) or fall behind by as much as 14 min 6 s (around February 12). It results from an apparent irregular movement of the Sun caused by a combination of the obliquity of the Earth's rotation axis and the eccentricity of its orbit. The equation of time is visually illustrated by an analemma.

Escapement - That portion of the movement that allows the motive power of the watch to "escape" slowly and in a regulated fashion, thus keeping time.

Fine Silver - Silver that is 999 fine or higher, meaning that it is 999 parts per 1000 pure silver.

Gear Train - The interconnected system of gears and pinions which transmits power from the mainspring to the escapement.

German Silver - A composition of nickel, copper and zinc. It contains no silver. Also known as Nickel Silver.

Guilloché - Engraving with a repetitive pattern (lines, waves, circles, etc)

Hairspring - The delicate, spiral-wound spring which governs the oscillation of the balance wheel and provides the fundamental timekeeping mechanism of the watch. Hairsprings can be "flat" or "overcoiled" in design. The shape of the overcoil or terminal curve of the hairpspring can have a significant effect on the positional accuracy of the watch. Hairsprings can be made of blue steel or other more exotic metal alloys such as "Invar" or "Elinvar" which are formulated to resist the adverse effects of temperature or magnetism.

Hunting Case - A pocket watch which has metal "lids" on both the front and back of the watch. See also "Cuvette".

Horology - The science of time and timekeeping, including clocks and watches.

Impulse Jewel - The jewel-pin that serves as the point of contact between the time-train and the balance wheel. Also called the roller jewel.

Jewel - A tiny donut-shaped "bearing" that supports (or caps) a wheel pivot to reduce friction. Usually made of synthetic ruby or synthetic sapphire. In general, the higher the jewel count, the higher the grade of the watch. 19-jewel or higher is considered a high-grade watch. The jewels themselves have no value as jewels, and contrary to popular myth, unscrupulous watchmakers will not "steal the jewels out of your watch."

Karat - A measure of fineness; 24 karat is fine gold. One karat equals 1/24 (.0417%), so that 14 karats is 14/24 fine gold and the balance 10/24 is alloy. 24K is pure gold. Jewelery is typically made from 18K or 14K gold, which contains other metals for strength. If the gold content of an alloy is less than 10/24 (10K) the object cannot be represented as karat gold. Not to be confused with "Carat" which is a unit of weight used in the measurement of gem-stones.

Lancashire Gauge - An arcane English system of measurement used for watches. For a more complete description of Lancashire Gauge and a table of watch sizes, click here.

Lever-set - A watch that is set by moving a small lever usually located under the bezel. A safety feature of Railroad watches that prevented accidental changes to the time. See also "Pendant Set".

Ligne - (French, pronounced "line") A unit of measurement used for (usually) Swiss and French watches. One Ligne is 2.2558291mm or 0.088812168 inches. There are 12 Ligne to one French inch (pouce, French for thumb) and 12 pouce to a French foot (Pied).

Lugs - Extensions on both sides of a wristwatch case where the bracelet or strap is attached.

Main Plate - Base plate on which all the other parts of a watch movement are mounted (part of the "ébauche").

Mainspring - The wound, flat metal spring which provides the motive power for the watch. Older mainsprings were "blue steel," but modern mainsprings tend to be made of alloys which are more resistant to breakage and corrosion.

Manual Winding - Refers to a watch with a manual mechanical movement, which needs to be wound by the wearer using the winding crown. This winds the mainspring up which then releases its energy to power the watch.

Mechanical Movement - A movement based on a mainspring which when wound slowly unwinds the spring in an even motion to provide accurate timekeeping. As opposed to a manual mechanical watch which needs to be wound on a consistent basis, an automatic mechanical requires no winding because of the rotor, which winds the mainspring every time you move your wrist (see our section on automatic watch maintenance for more details).

Minute Repeater - A watch which can additionally "repeat" the time, at the push of a button or move of a small slide on the side of the case, by striking the hours, quarter hours and minutes since the last quarter hour on small gongs inside the watch. See also "Repeater."

Movement - The watch's "works." As distinguished from the case.

Nickel Silver - A composition of nickel, copper and zinc. It contains no silver. Also known as German Silver.

Pallet - Sometimes called pallet fork. That portion of the escapement which connects the time train to the balance, and allows the power of the watch to escape at a predictable rate through the locking and unlocking action of the pallet jewels on the teeth of the escape wheel.

Pendant - The portion of the watch which holds the winding-stem and crown.

Pendant-set - A watch that uses the pendant to set the watch. See also "Lever-set".

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.

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.

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.

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.

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 eachother out.

Train - (see also Gear Train) The interconnected system of gears and pinions which transmits power from the mainspring to the escapement.

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 timezone/standard avoids errors and problems associated with different time zones and summer times operational in different countries.