Watchmaking Glossary

Amplitude:

Amplitude is the measure of the amount of rotation in the swing of the balance wheel, in either direction, usually expressed in degrees. In a running watch, the balance wheel swings or rotates clockwise and counterclockwise. Each swing in either direction is called a “beat”. Amplitude is the number of degrees of rotation of the beat. Amplitude is higher, typically in the range of about 270 to 315 degrees, when a watch is lying flat or in the “dial up” or “dial down” position. Amplitude usually falls when the watch is in a vertical position, primarily due to increased friction. Amplitude can also fall as the watch winds down and the mainspring delivers less power. Amplitude that is too high or too low, or that changes too much in different positions, can indicate a problem with the movement.

Antimagnetic:

Protected against the effects of magnetic fields, which can affect a movement’s precision by influencing the balance’s rate of oscillation. One way to protect against magnetism is to make the balance and balance spring of metals that either cannot be magnetized or are resistant to becoming magnetized (e.g., Elinvar or Nivarox hairsprings used in conjunction with brass, nickel or beryllium bronze balances). Other delicate components, specifically the lever, escape wheel and impulse roller, can also be made of nonmagnetic metals. Another way to protect against magnetism is to enclose the entire movement in a case made from a highly conductive alloy, which prevents magnetic fields from building up inside it. A watch can be described as antimagnetic if, within a magnetic field of 4,800 A/m (amperes per meter), it continues to run with a deviation of no more than 30 seconds per day. One symptom that suggests that a watch has been magnetized is a tendency to run slow. A magnetized watch can be “cured” (i.e., demagnetized) by a watch repairer using a choking coil.

Automatic:

A mechanical movement whose mainspring is wound by means of a built-in rotor that swings around its axis when the wearer moves his arm.

Balance:

The regulator, or oscillator, in a mechanical watch. The balance is a wheel that rotates back and forth on an axle, its motions governed by the coiling and uncoiling of the hairspring, or balance spring. The precision of the timepiece depends to a very large degree upon the construction of the balance. Most modern watches have balances that oscillate 21,600 or 28,800 times per hour (often abbreviated“vph” for “vibrations per hour”), but some have lower or higher frequencies, such as 18,000 or 36,000 vph.

Balance Spring:

The extremely thin, coiled spring that controls the swings, or oscillations, of the balance. The inner end of the hairspring is attached to the balance staff and the outer end to a stud on the balance cock. The spring’s elasticity ensures that the balance swings back and forth at a regular rate. The active length of the hairspring interacts with the momentum of the balance rim to determine the duration of each beat of the balance. This is why most watches are equipped with a regulator on the balance cock that can be adjusted to vary the active length of the hairspring. Lengthening the spring causes the watch to run more slowly; shortening it makes the watch run faster.

Bezel:

The ring around a watch dial that typically holds the glass or crystal covering the dial in place. Many watches have rotating bezels that can be turned to measure elapsed time or to indicate the time in a second time zone.

Bridge:

A flat, typically narrow metal piece secured to the plate at both ends and drilled with a hole or holes into which jewels may be fit that hold the rotating pivot(s) of a moving part or parts.

Caliber:

A specific watch-movement model, usually denoted by a number or alphanumeric name, as in Caliber 2824 (ETA’s famous automatic caliber) or Caliber 74.3 (Tourby´s new manual-wind caliber).

CDC (cotes de cirqulaires):

Decorative rounded stripes  on the plates, bridges, cocks or rotors of many watches. 

Center or sweep second hand:

A seconds hand mounted in the center of the dial rather than in a subdial. The arbor of the center wheel is hollowed out to make room for the shaft of the seconds hand.

Chronometer:

A watch that has passed a battery of timing tests administered by an official chronometer-certification agency such as COSC. Decades ago the word was used differently, and meant a timepiece with a so-called “chronometer” or “detent” escapement, or any very accurate timepiece.

COSC:

Also known as “C.O.S.C.”. Abbreviation for “Contrôle officiel suisse des chronomètres”, French for “Swiss chronometer testing bureau.” COSC is a Swiss-government-sponsored agency that tests watches submitted to it and issues chronometer certificates to those that are precise enough to meet COSC standards. COSC operates three testing facilities: in Bienne, Le Locle and Geneva.

Cotes de Geneve (CDG):

Decorative stripes on the plates, bridges, cocks or rotors of many watches. Geneva waves are also called “Geneva stripes” or “côtes de Genève” (Geneva ribbing).

Crown:

A knob on the side of the case that is turned to wind the watch’s mainspring, set its hands and, in watches equipped with a calendar, correct its date display. In water-resistant watches, the crown is frequently screwed into the case.

Crystal:

The word has two watch-related meanings. One is the transparent, protective cover over a watch dial. These covers can be made of plastic, mineral glass or synthetic sapphire. The other meaning of “crystal” is the tiny piece of quartz that regulates the timekeeping of a quartz watch.

Dial:

The face of a watch. Some dials have within them smaller dials for displaying such information as the date, the phase of the moon, or, on a chronograph, the elapsed minutes, hours, or running seconds. These dials are called “subsidiary” dials, or “subdials.”

Escapement:

The mechanism in a movement that transfers power from the mainspring via the wheel train to theregulator, thus maintaining the regulator’s oscillations. The parts of a standard escapement are the escape wheel and pinion; the lever (also called the “anchor”), with its pallet arms and pallets; the pallet staff; the banking pins; the fork, with its safety pin; the impulse roller, with its impulse pin; the safety roller and the balance staff.

Fine Adjustement:

Precise adjustment of a watch’s rate by means of a device such as a swan’s neck regulator or eccentric screw.

Geneva Waves:

Decorative stripes on the plates, bridges, cocks or rotors of many watches. Geneva waves are also called “Geneva stripes” or “côtes de Genève” (Geneva ribbing).

Guilloche:

A type of decorative pattern, such as barleycorn or sunburst, found on some watch dials and plates. Genuine guilloché is produced using an elaborate engraving machine and is also known as “engine turning.” Guilloché can also be simulated with a less-expensive stamping process.

Hacking Second:

Also known as hack or stop seconds. A watch that “hacks” or that has “hacking seconds” is one in which the seconds hand stops when the crown is pulled out. Hacking is typically achieved when pulling the crown out to the time-setting position causes a brake or lever to come into contact with the rim of the balance wheel, causing it to stop and to be held in position. Hacking allows the watch to be more easily set to a reference signal, or synchronized with second timepiece. Pushing the crown in releases the brake or lever, allowing the balance wheel to move freely.

Hairspring:

The extremely thin, coiled spring that controls the swings, or oscillations, of the balance. The inner end of the hairspring is attached to the balance staff and the outer end to a stud on the balance cock. The spring’s elasticity ensures that the balance swings back and forth at a regular rate. The active length of the hairspring interacts with the momentum of the balance rim to determine the duration of each beat of the balance. This is why most watches are equipped with a regulator on the balance cock that can be adjusted to vary the active length of the hairspring. Lengthening the spring causes the watch to run more slowly; shortening it makes the watch run faster.

Hand Wound:

A mechanical movement whose mainspring must be wound by turning the crown. Compare withautomatic movement. Also called a manual-wind movement.

Incabloc Shock Proof:

A brand of mechanical-watch-movement shock absorber. Because a watch balance staff is extremely delicate, its pivots are protected from jolts and knocks by devices incorporating flat springs such as those made by Incabloc (Kif is another well-known brand of shock-absorber). Incabloc shock absorbers can be recognized by their springs’ distinctive lyre shape.

Jewels:

Synthetic rubies used in a watch movement. Some jewels are used as bearings to reduce friction. They’re set in holes drilled into the movement plate and bridges, and hold the rotating pivots of the movement’s gears and wheels. Jewels are also placed on top of the balance-pivot jewels (these are called “endstones”) where they rest against the tips of the balance staff pivots. Because of their hardness (ruby, a type of corundum, measures “9″ on the Mohs hardness scale where diamond measures 10), jewels are also used in the escapement to engage the teeth of the escape wheel (these are called “pallet jewels”) and on the roller (this is called the “roller jewel”).

Limited Edition:

A watch produced in a limited quantity and usually numbered to show its place in the series.

Lugs:

The parts of the case to which a watch strap or bracelet is attached. Also known as the “horns.”

Mainspring:

A spiral spring that provides power to a mechanical movement. After being wound either manually or by an automatic winding system, the mainspring, which is housed in a barrel affixed to a toothed disk, gradually uncoils. As it does so, it causes the barrel to rotate slowly on its arbor, keeping the watch’s gear train in motion. Most watch mainsprings are made of Nivaflex, an alloy that is elastic and relatively resistant to breakage.

Manual Wind Movement:

A mechanical movement whose mainspring must be wound by turning the crown. Compare with automatic movement.

Mechanical Movement:

A watch that is powered by a mainspring and regulated by a balance. There are two types of mechanical watch: hand-wound and automatic.

Movement:

The movement is the complete inner mechanism of a watch. Specific models of movements are often referred to as calibers.

Pallet:

One of two small pins in a lever escapement that mesh with the teeth of the escape wheel. Pallets are usually made of synthetic ruby.

Perlage:

A type of decoration applied to watch movements. It consists of small, overlapping circles. The word is French and means, literally, “pearling.”

Power Reserve:

The length of time that a mechanical movement will run without needing to be rewound. Mostmechanical watches have power reserves of 36 to 48 hours, although some have power reserves of a week or even longer.

Rotor:

A pivoted eccentric weight in an automatic watch that swings back and forth when the wearer moves his arm, thus winding the mainspring.

Screw-Down Crown:

A threaded winding crown that screws tightly into the case and prevents water and dust from entering.

SCDG (small cotes de Geneve):

Decorative stripes on the plates, bridges, cocks or rotors of many watches. Geneva waves are also called “Geneva stripes” or “côtes de Genève” (Geneva ribbing).

Skeletonized Movement:

A movement whose plate, bridges, cocks, barrel and rotor (if present) have been pierced so that only metal that is absolutely necessary for each part’s function remains. Skeletonized parts make it possible to look into (and through) the movement.

Stop-Second:

A mechanism that stops the movement so that the time can be synchronized to a time signal with to-the-second precision. To accomplish this, the wearer pulls the crown out the instant the seconds hand reaches the “12.” When he hears the time signal, he immediately pushes the crown in and the watch starts running again. This is also called a “hacking” feature.

Swiss Made:

A term that, according to Swiss law, applies to watches meeting the following requirements: 1. The watch has a Swiss movement, meaning that at least 50% of the movement’s components (as determined by the components’ value) are made in Switzerland and the movement is assembled and inspected there and 2. The watch itself is assembled and inspected in Switzerland.

Tritium:

An isotope of hydrogen that is used to make watch hands and indices glow in the dark. Until a few years ago, hands and indices were often painted with tritium paint. But because tritium is mildly radioactive, and feared by some to be a health hazard, tritium paint is no longer used on dials. (The consensus among scientists is that, despite consumers’ apprehensions, tritium paint on watch dials presents no danger.) Instead, some watch companies affix tritium-gas-filled tubes to their dials’ hands and indices. The tubes are more acceptable commercially because the gas is contained and hence emits even less radiation than tritium paint does. Tritium is unlike other luminous substances used on watch dials (Super-LumiNova is the most common of these) because it does not require exposure to light to make it glow: it will do so for years without fading appreciably.

Vibrations VPH:

In a watch movement with a balance wheel, one vibration is a single swing of the balance wheel. A vibration is one-half of an oscillation, or a semi-oscillation. So, one swing of the balance wheel in either direction, for example clockwise, is one vibration or semi-oscillation, and two swings, for example clockwise then counter-clockwise, is an oscillation.

The frequency of a watch movement can be expressed in Hertz (Hz) or in vibrations per hour (vph), which is also sometimes referred to as A/h. The frequency in Hertz is the number of oscillations per second. Double the hertz figure to get the number of vibrations or semi-oscillations per second. Multiply that number by 3600 (the number of seconds in an hour) to get the vph.

The most common frequency for modern mechanical wristwatch movements is 4 Hz, or 28,800 vph. A watch ticking at 4Hz makes 4 oscillations per second, or 8 semi-oscillations (or vibrations) per second. There are 60 seconds in a minute, so this watch would tick at 480 semi-oscillations (or vibrations) per minute. Multiplying the 480 vibrations per minute by the 60 minutes in an hour yields the 28,800 vph figure. Since this watch ticks 8 times per second, a chronograph in a 28,800 vph watch can time events to the nearest 1/8 of a second.

Following this formula, a watch with a rate of 2.5 Hz or 18,000 vph can time events to the nearest 1/5 of a second. A rate of 3 Hz or 21,600 vph yields accuracy of 1/6 of a second. A watch with a rate of 36,000 vph or 5 Hz can time to the nearest 1/10 of a second.

WR (Water Reistant):

Able to withstand contact with water without suffering damage. Watches have various degrees of water-resistance. A water-resistance level of 30 meters means the watch can withstand splashes of water. A level of 50 meters means that it can be worn for swimming in shallow depths. A level of 100 meters means it can be worn snorkeling and a level of 200 meters or more means it can be worn scuba diving. The numbers “50,” “100,” etc., refer to the amount of water pressure the case can withstand, not the depth to which the watch can actually be worn. That’s because wearing a watch underwater subjects it to far greater pressure, due to the motion of the wearer’s arm through the water, than the watch encounters when it is absolutely stationary, as it is when its water-resistance level is determined.

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