Timepiece Glossary

ALARM
A complication that sounds a signal at a predetermined time.

AUTOMATIC WINDING
This referred to winding that occurs through motion on the wearer’s wrist, rather than through winding the watch manually. An automatic watch that isn’t worn for a couple days will need to be wound again to get started again.

APERTURE
A small opening in the dial that displays certain information such as date, day, month or moon-phase.

ANTI-MAGNETIC
A device that is not affected by magnetic fields.

BALANCE
The heart of a mechanical watch movement. The mainspring provides the energy and the balance (coupled with the hairspring) swings to divide time into equal parts.

BALANCE SPRING
A very small spring in a mechanical watch that returns the balance wheel back to its neutral position.

BALANCE WHEEL
A part of a mechanical watch that oscillates and divides time into equal portions.

BEZEL
The ring around the crystal on the top portion of a watch. It is usually made of metals such as gold, gold-plate, platinum or stainless steel. It holds the glass or crystal in place.

BI-DIRECTIONAL ROTATING BEZEL
A bezel that can be moved either clockwise or counter-clockwise. Used to make mathematical calculations or keeping track of elapsed time.

CALENDAR
A feature that shows the day of the month, and often the day of the week. Some calendar watches show the date on sub-dials while others use a scale on the outside edge of the watch dial.

CALIBER
Also known as calibre, the caliber is the size or style of a watch movement.

CASE
The container that protects the watch movement. It also gives the watch an attractive appearance. Cases come in many shapes, round, square, oval, tonneau and rectangular.

CASEBACK
The underside of a watch that lies against the skin. Some casebacks are made of crystal allowing you to view the watch movement.

CHRONOGRAPH
A stopwatch complication that can be started and stopped via pushers to time and event.

CHRONOMETER
An instrument for measuring time very accurately. For a Swiss watch to be called a chronometer, it must meet very high standards set by the C.O.S.C. (Controle Officiel Suisse des Chronometres). The requirements are 15 days and nights at five different positions and temperature changes.

COTES DE GENEVE
A regular wave pattern obtained by engine-turning and polishing.

CROWN
A button, often fluted, on the outside of the watch case used to wind the mainspring in mechanical watches. It is also used to set the time, when pulled out, and for setting a watch calendar. A screw-down crown is used to make the watch more water resistant and to help keep out dust.

CRYSTAL
A transparent cover that protects the watch dial. Crystals are made of glass, plastic or synthetic sapphire. Non-reflective coatings on some crystals prevents glare.

DAY-DATE
A watch that indicates the day of the week as well as the date.

DAY/NIGHT INDICATOR
A colored or shaded band on a world time watch, which shows the time zones that are in daylight and those in darkness.

DEPLOYANT BUCKLE
A buckle that fastens to the watch strap and opens and fastens using hinged extenders. Invented by Louis Cartier in 1910. A deployant buckle is easier to put on and remove than a tang buckle. Deployant comes from the verb “deployer” which means to unfold.

DIAL
A plate, with a metal base and visible through a crystal, that carries certain indication, such as the hours, minutes and sometimes seconds.

ESCAPEMENT
A device in a mechanical watch that controls the motion of the hands by controlling wheel rotation.

ETA
The leading manufacturer in Switzerland for movements used in many Swiss brands.

FLY-BACK CHRONOGRAPH
In a chronograph, there is an additional seconds hand that moves with the seconds hand and can be stopped independently and then made to catch up (“fly-back”) with the other constantly moving seconds hand.

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
A system of gears that transmit power from the mainspring to the escapement.

GRAND SONNERIE
A Repeater that sounds the hours and quarter hours by pressing a lever.

GREENWICH MEAN TIME (GMT)
The standard for which all other 23 time zones are based off of and sometimes referred to as UTC.

GUILLOCHE
Surface decoration or texture. An even pattern is cut, usually on the dial.

HAND
The indicator that moves over the dial to point at the hour, minute or second. Watches generally have three hands to show the hours, minutes and seconds. Hands can have very different shapes: pear, Breguet, sword, skeleton, baton, arrow, etc.

HELIUM ESCAPE VALVE
Prior to surfacing from great depths in a pressurized enclosure, such as diving bell, toxic gases that have been formed in the enclosure are removed and helium is mixed into the air. The helium molecules are lighter than air and can therefore penetrate the watch. When the pressurized enclosure surfaces and is depressurized the helium rushes out of the watch so quickly that the glass on the watch pops out as well. The watch was built to withstand external pressure, not internal pressure. The glass popping out can be avoided by opening the Helium Escape Valve on the watch during resurfacing, which allows the helium to escape but prevents water from entering the watch.

HOROLOGY
The science of the measurement of time.

HOUR MARKERS
Arabic numerals, Roman numerals or symbols placed around the dial to mark the hours.

JEWELS
Sapphire or Rubies that reduce friction by acting as bearings for gears in a mechanical watch.

LUGS
Sometimes referred to as horns, lugs are projections on the watch case. There is a spring bar between the lugs that is used to fix the strap or bracelet to the case.

LUMINESCENCE
Luminescence refers to emitting rays of light. A luminescent material is deposited on numbers and hands in order to read the time in the dark.

MAINSPRING
Contained in the barrel, the mainspring is the driving flat-coiled spring of a watch that supplies power.

MANUFACTURE
A watch company that uses at least one of its own movements that has been manufactured in house.

MILITARY TIME
Time that is measured in 24-hour segments. (IE: 10pm is referred to as 2200 hours).

MINERAL CRYSTALS
Heat hardened glass about ten times harder than plastic. Extremely scratch resistant but must be replaced if they do scratch.

MECHANICAL MOVEMENT
A mechanical movement is powered by a main-spring and works with the balance wheel.

MOVEMENT
The inner mechanism of a watch that keeps time and powers the watch’s functions.

PERPETUAL CALENDAR
A calendar complication that adjusts the watch’s calendar for the varying length of months as well as leap years.

POWER RESERVE INDICATOR
A feature of a mechanical watch that shows the remaining power in a watch movement, indicating the length of time until the timepiece will need to be wound again.

PVD
Physical vapor deposition is a thin coating applied to a case to add color for aesthetic purposes.

QUARTZ MOVEMENT
A movement that is powered by a quartz crystal. The crystal oscillates to power the timepiece.

QUICK-SET
Also referred to as Quick-Date, it is a mechanism to set the date directly to avoid having to turn the hands over 24 hours.

REGULATOR
A part of the movement that makes time more accurate by regulating beats by speeding them up or slowing them down.

MINUTE REPEATER
A device that chimes the time upon depressing a slide lever.

RETROGRADE HAND
A hand with a tip moving over a portion of the arc of a circle instead of an entire circle. When it reaches the end of its path, it instantly returns to its point of departure.

RIDER TABS
Four markers placed around the bezel used as points of reference to mark a departure time or a set time one wishes to remember.

ROTOR
Part of an automatic watch that winds the mainspring by constantly rotating.

SAPPHIRE CRYSTALS
Sapphire crystals are 2-3 times harder than mineral glass and virtually scratch-proof. They are more brittle so are more likely to crack or shatter than mineral. Replacement cost is substantially higher than for mineral crystals.

SCREW BACK
The back of the case has a thread so that it can be screwed into the case.

SCREW-DOWN CROWN
A crown that screws down into the case to make the watch more water resistant and to help keep out dust.

SHOCK ABSORBER
Resilient bearing in a watch that is intended to take up the shocks received by the balance staff and protect its delicate pivots from damage.

SHOCK RESISTANCE
A watch’s ability to withstand an impact equal to being dropped onto a wooden floor from a height of 3 feet.

SKELETON WATCH
The case, dial and various parts of the movement have been cut away allowing the main parts of the watch to be seen. A crystal is mounted on both the front and back of the watch.

SLIDE RULE
A rotating bezel that can multiply or divide two numbers, convert miles/KM, convert exchange rates, etc. An example is a dollar to Euro converter to calculate rate of descent or fuel consumption for pilots.

SMALL SECONDS DIAL
The seconds are displayed by a hand in a small subsidiary dial and not from the center of the timepiece.

SONNERIE
A variation of a minute repeater that sounds the time automatically every hour (petite sonnerie) or quarter hour (grande sonnerie).

SPLIT SECONDS CHRONOGRAPH
A watch that possesses two hands, one of which can be stopped to indicate an intermediate time while the other hand continues to run.

SPRING BAR
A spring loaded metal bar mounted between the case lugs (horns) used to attach a strap or bracelet.

STANDARD TIME
The time that is kept locally in each of the time zones when it is not daylight savings time.

STEM
The shaft that connects to the movement’s winding mechanism. The crown is fitted on the opposite end.

STRAP
A strip or band of leather or rubber that holds the watch to the wrist. It must be non-metal to be considered a strap; a metal version is referred to as a bracelet.

SUB-DIAL
A small dial placed inside the main dial on a watch’s dial. Watches can have as many as four sub-dials (auxiliary dials). They give information not provided by the main watch dial such as chronographs, alarm, dual time zone, and calendar.

SWEEPING SECONDS HAND
A second hand that is mounted in the center of the dial, instead of a sub-dial, and “sweeps” the entire dial of the watch.

SWISS MADE
A watch can only be considered to be Swiss made if, (1) its movement is Swiss; (2) its movement is cased up in Switzerland and (3) the manufacturer carries out the final inspection in Switzerland.

TACHOMETER
A tachometer, also referred to as a Tachymetre, is a graduation on dial of a chronograph which enables one to determine average speeds or hourly production on the basis of an observation period of under sixty seconds.

TANG BUCKLE
Conventional feed through buckle (like a belt buckle).

TIME ZONES
Time zones refer to the twenty-four regions or divisions of the globe. Our time zone here in Minnesota will be indicated by either Chicago or Mexico City.

TOURBILLON
A device that eliminates errors in timekeeping by balance the horizontal and vertical positions of the balance wheel.

UNI-DIRECTIONAL ROTATING BEZEL
A bezel that indicates elapsed time, often found on divers watches. It moves only in a counter-clockwise direction. If a diver is timing his remaining air supply and knocks the bezel by mistake, it can only move in one direction so that the error will only be on the side of safety.

WATER RESISTANCE
The ability of a watch to withstand (resist) splashes of water on the timepiece. This will indicate the depth that a watch can be worn underwater.

WHEEL
Also referred to as a pinion, the wheel is a circular part that revolves around an axis to transmit power.

WINDING
Winding is the action of tightening the mainspring of a watch. This is done by hand (turning the crown) or automatically (by the motion of the rotor).