Watch Glossary and Terms with Images

InvarA steel-nickel alloy whose low coefficient of expansion was discovered by Charles Edouard Guillaume. Invar (abbreviation of invariable) belongs to the Elinvar family of metals which encompasses ferronickel alloys whose thermoplastic coefficient is a negligible -10°C to +30°C. These alloys are used to make compensation balances for watches.IsochronismEqual periods of time. A watch's ability to maintain its rate as the mainspring unwinds.J ImagesJewelBearing, endstone or pallet used for reducing friction. Generally made of synthetic material, except for the precious or semi-precious stones (ruby, sapphire, garnet) which are sometimes used in "de luxe" watches.JewelsThe international term for the jewels (rubies) in a watch movement that are used as bearings for pivots to reduce friction. The movement of a quality watch has between 15 and 21 jewels.Jumping hourA means of display in which the hour, shown through an aperture, instantly changes every 60 minutes.K ImagesKaratThe unit of measurement of the purity of a gold alloy. A 1k alloy contains 1/24th of its weight in pure gold. An 18k alloy is 18/24th pure gold. Pure gold is 24k.GildThe case but also the movement;s plate and bridges can be gilded.Glass, CrystalThin plate of glass or transparent synthetic material, for protecting the dials of watches, clocks, etc.GuillocheDecoration found on the dials of high-end watches.H ImagesHackingA feature that stops the second hand when the stem is pulled out as far as it will go. This allows you to set the exact time.HandIndicator, usually made of a thin, light piece of metal, very variable in form, which moves over a graduated dial or scale. Watches usually have three hands showing the hours, minutes and seconds.HorologyScience of time measurement, including the art of designing and constructing timepieces.I ImagesImpulseMovement transmitted by a mechanical part. In a lever escapement, the impulse occurs via the impulse su***ce of the wheel tooth and the pallet.IndicatorA watch;s indicators are its dial and hands.