G

Gasket - most water-resistant watches are equipped with gaskets to seal the case-back, crystal and crown from water infiltration.  Gaskets should be checked every couple of years to maintain water resistance.

Gear train - the system of gears that transmits power from the mainspring to the escapement.

Geneve stripes - see Côtes de Genève.

Glucydur - an anti-magnetic alloy that expands very little when exposed to heat. This quality makes glucydur useful in making balances.

G.M.T. - see Greenwich Mean time.

Goldplating - an electro deposited layer of gold.  The thickness is measured in microns.

Grand Sonnerie - A watch that strikes the hours and quarter hours when a button is pushed.

Gray market - unauthorized sellers of new watches.

Greenwich Mean Time - the standard for timekeeping that was introduced in England in 1880 and used as the basis for calculating standard time throughout the world.  It reflects the mean solar time along the Earth's prime meridian. 
(The prime meridian is 0° longitude).  The prime meridian runs through the Greenwich Observatory outside of London, England.
 

Guilloche - surface decoration. An even pattern is cut, usually on the dial.