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.

GENEVA SEAL
Poincon de Geneve.

GLUCYDUR
Bronze and beryllium alloy used for high-quality balances. This alloy assures high elasticity and hardness values; it is non-magnetic, rust-proof and has a very reduced dilatation coefficient, which makes the balance very stable and assures high accuracy of the movement.

GMT

Abbreviation for Greenwich Mean Time. As a feature of watches, it means that two or more time zones are displayed. In this case, the second time may be read from a hand making a full rotation in a 24-hour ring (thereby also indicating whether it is a.m. or p.m. in that zone).

GOING TRAIN

Train.

GONG
Harmonic flattened bell in a steel alloy, generally positioned along the circumference of the movement and struck by hammers to indicate time by sounds. Size and thickness determine the resulting note and tone. In watches provided with minute-repeaters, there are often two gongs and the hammers strike one note to indicate hours, both notes together to indicate quarters and the other note for the remaining minutes. In more complex models, euipped also with en-passant sonerie devices, there may be up to four gongs producing different notes and playing even simple melodies (such as the chime of London's Big Ben).

GRAND (or Great) COMPLICATIONS
s. Complication

GUILLOCHE

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 similiar 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 guilloche) are very intricate and expensive to produce, which is why most dials decorated into this fashion are produced by stamping machines.