Glossary  A - B   C - F   G – L   M - P   Q - S   T - W

Gear train   A mechanical watch's gear train transmits energy from the mainspring to the escapement. The gear train comprises the minute wheel, the third wheel, the fourth wheel, and the escape wheel.     GMT   GMT, or Greenwich Mean Time, is based on the globe being divided into 24 time zones as established in the Meridian Conference of 1884. The zero meridian runs through the Royal Observatory in the London suburb of Greenwich (pictured). In contemporary watch terminology, GMT is often used to describe a wristwatch that displays a second time zone or a 24-hour indication.     Guilloché   A surface decoration usually applied to the dial and the rotor using a grooving tool with a sharp tip, such as a rose engine, to cut an even pattern onto a level surface. The exact adjustment of the tool for each new path is controlled by a device similar to a pantograph, and the movement of the tool can be controlled either manually or mechanically. Real guillochis (the correct term used by a master of guilloché) are very intricate and expensive to produce, which is why most dials decorated in this fashion are produced by stamping machines. Breguet is one of the very few companies to use real guilloché on every one of its dials.     Index   A regulating mechanism found on the balance cock and used by the watchmaker to adjust the movement's rate. The index changes the effective length of the balance spring, thus making it move more quickly or slowly. This is the standard index found on an ETA Valjoux 7750.     Jewel   To minimize friction, the hardened steel tips of a movement's rotating gear wheels (called pinions) are lodged in synthetic rubies (fashioned as polished stones with a hole) and lubricated with a very thin layer of special oil. These synthetic rubies are produced in exactly the same way as sapphire crystal using the same material. During the pocket watch era, real rubies with hand-drilled holes were still used, but because of the high costs involved, they were only used in movements with especially quickly rotating gears. The jewel shown here on a bridge from A. Lange & Söhne's Double Split is additionally embedded in a gold chaton secured with three blued screws.     Luminous substance   Tritium is a slightly radioactive material used to coat hands, numerals, and hour markers on watch dials in order to make reading the time in the dark possible. Watches bearing tritium must be marked as such, with the letter T on the dial near 6 o'clock. It has now for the most part been replaced by nonradioactive materials such as SuperLumiNova and Traser technology (as seen on this Ball timepiece, a pioneer in the technology) due to medical misgivings and expected governmental regulation of its use.

Courtesy of Wristwatch Annual 2006 © Abbeville Press  A - B   C - F   G – L   M - P   Q - S   T - W