Gear train A sequence of gears or small toothed wheels arrayed to transmit energy from the mainspring to the escapement or to a striking, chiming or musical mechanism. The gear train comprises the minute wheel, the third wheel, the fourth wheel and the escape wheel. The timekeeper receives energy as a result. Some watches have more than one gear train, for example, Breguet’s Tradition Independent Chronograph ref. 7077 is equipped with two independent gear trains: one for the time and one for the chronograph.

GMT or Greenwich Mean Time In horology, the abbreviation “GMT” or “GMT watch” refers to an additional time zone displayed by means of a 24-hour scale. A second hand on the dial, known as the 24-hour GMT hand, serves as the reference time and is co-axially located at the centre of the dial. The 24-hour scale may or may not be rotatable. True GMT watches are considered to be those that can track at least two time zones using central hour hands that are aligned to 12-hour and 24-hour scales.

Note: The Rolex GMT-Master, produced from the mid-1950s to 1999, and the Rolex GMT-Master II, produced from the early 1980s to the present, are perhaps the most iconic and recognisable examples of true GMT wristwatches for pilots and frequent travellers. The Rolex GMT Master and Rolex GMT-Master II both have bi-directional rotatable bezels that enable the user to view GMT at a glance or rotate the bezel plus/minus a specific number of hours relative to GMT to identify a second time zone altogether. The Rolex GMT-Master II features a local “jumping” hour hand that can be independently adjusted without disturbing the 24-hour hand or local minute hand and may concurrently be used to adjust the date either forwards or backwards with no additional wear and tear to the movement (caution: not all movements accommodate this feature and some can be damaged if wound backwards). The local “jumping” hour hand enables the user to track two different time zones simultaneously (without moving the bezel), and if the user were to rotate the bezel thereafter (assuming that the 24-hour hand is set to GMT), he or she can track up to three
different time zones.

The Rolex Explorer II is similar to the Rolex GMT-Master II, except that its 24-hour scale is not on a rotatable bezel.

A GMT watch is not to be confused with a dual-time watch, which customarily displays two time zones each in a 12-hour format. A dual-time watch may also qualify as a pilot’s watch, but is intended for those who need to adjust both times more frequently.

Gong-spring A length of wire that produces a sound when struck by a hammer or striker. One end is fixed to a firm base and the wire vibrates to produce a sound or musical note on the striking action. The gong-spring was invented by Breguet and first applied in a striking repeating watch in 1783. Breguet’s invention represented a giant leap in watchmaking because the gong-spring increased the optimisation of sound and pushed the boundaries of miniaturisation. It has been almost universally adopted by watchmakers ever since.

Note: Breguet formerly used steel for the gong but has found that gold produces a richer quality of sound. This has the added bonus of bringing the resonance into alignment with the watch case where the latter is constructed in the same precious metal as the gong-spring. Gongs may also be found in clocks for both chiming and striking the hours, as well as alarm watches.

Gregorian Calendar So named after Pope Gregory XIII (7 January 1502 – 10 April 1585) as a reform of the Julian Calendar, decreed by the papal bull Inter gravissimas of 24th February 1582. The standard was gradually adopted throughout the Holy Roman Empire and in England by Act of Parliament in 1752. It was not until after World War I that the Gregorian Calendar finally became the internationally accepted civil calendar.

Guillochage The technique of pattern engraving by an artisan using hand-driven machine tools, such as a rose engine, via a grooving tool with a sharp tip onto a level surface. This ornamentation results in patterns that can be curved, interlaced, symmetrical or geometrical and the machine may be operated either manually or automatically. Breguet is famous for its guillochis in the pocket watch and wristwatch era; in fact, it was Abraham-Louis Breguet who first introduced guilloché to watch dials. Genuine guilloché epitomises the handcrafts and is both intricate and beautiful to look at. It represents a true labour of love and is often seen on Breguet’s dials and rotors. Breguet’s master guillochers have also perfected the art of working with curved surfaces, culminating in the mastery of Breguet’s Héritage Tourbillon ref. 5497, which is a spherical watch set in a curved tonneau shaped case with spherical crystal and a spherical chapter ring to match – a tour de force.

Note: Guillochage is not to be confused with freehand engraving such as Le Ciselage (carving) and Le Gravage (engraving). Ciselage is reserved for Breguet’s rarest timepieces such as the minute repeater, perpetual calendar and a few tourbillon wristwatches. Gravage engraving is often found on many movements with the name “Breguet” engraved by hand onto the rotor or plate of the movement.

Horology The study and measurement of time as well as the art and science of making clocks and watches. Abraham-Louis Breguet fused the art and science of watchmaking and timekeeping inextricably, so much so that Breguet continues to be a leader and an innovator in the field of high horology.

Index A movable lever found on the balance cock of a clock or watch used to regulate the timekeeping. The watchmaker can thus fine-tune the rate of a movement by increasing or decreasing the active length of the balance spring. This can be seen by the small plus and minus signs which are engraved on the index.

Jewel Jewels are synthetic rubies produced in the same way as sapphire crystals. The stones are then polished and lubricated with an ultra thin layer of special oil. Natural ruby was used in pocket watches but these were expensive to buy and work. Synthetic rubies can now be fashioned in superb quality and are used throughout the watch industry. Jewels are also tiny carved discs with or without a hole in the middle used in the axes of various wheels to reduce friction in the movement. The most important jewels or rubies are reserved for key axes like the balance which in modern timepieces are coupled with a shock absorption system.

Jump hours An hour hand or ‘digital’ hour display that jumps from hour to hour, rather than sweeping. Quartz watches fall into this category by default since the hour ‘jumps’ on the hour every time. Jump hours lend flair to mechanical movements making the ‘digital’ hour display fun and contemporary to look at. Also called a ‘jumping dial’ wherein hours and minutes may be advanced one division at a time. A seconds dial may or may not feature as part of a jump hours mechanism.

Luminous material Material that is used to store up photons in order to illumine the dial on a watch or clock to aid readability in low light conditions. The idea is that even a little exposure to natural or artificial light will activate the luminous material so that the wearer can clearly discern the time for a period even in pitch darkness. Luminous material can be used for Arab/Roman Numerals, hour markers, hour and minute hands and even on the second hand as well as sub-dials.

Note: Early luminous material was radioactive such as radium; dials painted with tritium were later used and though radioactive are far less dangerous and often marked with a ‘T’ on the dial at six o’clock. Nowadays, many brands use Super-LumiNova which is a safe, non-radioactive replacement for its predecessors developed in the mid-1990s. The best luminescent modern dials perform easily for 10-20+ years.

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