Aperture

A small opening in the dial. In an aperture watch, various indications such as the month, moon phase, day, date, hour, minute, etc. are visible through these openings.

Briolette

A drop shaped gemstone cut that has many triangular facettes.

Count wheel (Locking plate)

A wheel with alternating notches and raised portions which controls the number of hours struck.

Exterior

The different parts (case, dial, hands, crystal, crown, etc.) that help to give the watch its finished and functional appearance.

Fresh water cultured pearl

A cultured pearl that was formed in a freshwater mussel.

Girdle

The girdle is the widest perimeter of a gemstone that separates the top (crown) and the bottom (pavilion) of a cut gem.

Hessonite

A brown to orange gemstone variety of grossular garnet. This transparent stone has a hardness of 6.5 - 7 and a specific gravity of 3.6. This stone is not enhanced.

Imperial jade

An emerald green variety of jadeite, Imperial jade is very sought after in Asia. It comes from one mine in Myanmar (Burma).

Jeweller

In its original, eighteenth-century meaning, a jeweller is an expert in the art of mounting precious stones in gold, silver and, later, platinum so as to bring out their full beauty and sparkle....

Karrusel

A device similar to the tourbillon, the difference being that the cage is driven by the third wheel. Invented by Bonnicksen, a Danish watchmaker established in London.See complication.

Labradorite

A variety of plagioclase feldspar that has a greyish background with flashes of colour called labradorescence. It is used as watch dials. Labradorite has a hardness of 6 to 6.5 and a specific...

Micron

A metric unit of length equal to one thousandth of a millimetre or one millionth of a metre. The watch industry often expresses tolerances in microns.

Nephrite

A family of the jade group of ornamental gemstones. Nephrite is slightly softer that jadeite and is often veined.

Observatory chronometer

A chronometer which has received an official rating certificate from an observatory.

PVD

Physical vapour deposition, a technique for coating metal.See electroplating and plating.

Quartz

Silicon dioxide. Also called rock crystal. Quartz has the specific property of vibrating at a very high frequency (32 MHz) placed under electric current. Under certain conditions, it...

Rotor

A semi-circular disc that freely rotates with each movement of the arm to automatically wind the mainspring. Its own weight returns it to a vertical position.A specific system multiplies...

Spinel

A gemstone found in every pastel colour. The red variety was often mistaken for ruby. It has a hardness of 8, a specific gravity of 3.58-4.06, and a refractive index of 1.72.

Terminal coil

The incurved ends of the balance-spring to improve isochronism. Invented by Breguet and perfected by Phillips and others, hence often referred to as a "Phillips curve" or "Breguet overcoil".

Universal Time (UT)

Since 1972, a continuation of Greenwich Mean Time (GMT) which is mean solar time at the Greenwich meridian. Universal Time (UT) is a measurement of time based on the Earth's...

Vermeil

Silver covered with a thin layer of gold.

Wheel-cutting engine

A machine for cutting the required number of teeth into an unfinished gear after marking the position of each tooth with a dividing plate.

Year

A four-digit indication of the current year that changes automatically at midnight on December 31st.

Zinc

A metal applied by electrodeposition (electroplating) to protect iron and steel.