Reading this glossary
How to read an entry
Each term carries its status. Verified means a standards body, metrology institute or museum defines it and is quoted. Open question means the authority exists but part of the answer sits behind a paywall. No authority defines this means the term is in universal trade use and nobody official has fixed its meaning, 15 of 80 terms here are in that position, and each one lists what was checked.
That last category is the point of the glossary, not a gap in it. "Power reserve" and "complication" appear on every brand's website and in no standard.
Standards and certification
Chronometer
A precision rating awarded to a watch or movement by a neutral testing body, not a type of watch and not a function.
Divers' watch
A defined category under ISO 6425:2018, with requirements a watch must meet, not a style of watch.
Magnetic resistance
Covered by ISO 764:2020, which addresses everyday magnetic fields, not the high-field resistance some brands certify separately.
Master Chronometer
A Swiss federal certification of the finished, cased watch: distinct from chronometer certification, which is generally of the movement.
Poinçon de Genève
A state-backed Geneva hallmark for craftsmanship and durability, guaranteed by the State of Geneva and administered by TIMELAB.
Shock resistance
ISO 1413:2016 defines it by a specific simulated fall: one metre onto a horizontal wooden floor.
Water-resistant watch
Covered by ISO 22810:2010. What the depth marking means is less settled than the internet suggests, and this entry says exactly what is and is not documented.
How a watch works
Annual calendar
A calendar mechanism that distinguishes 30-day from 31-day months but not leap years, so it needs one correction a year at the end of February.
Automatic
A mechanical watch wound by the motion of the wearer's arm through a pivoting weight.
Balance wheel
The oscillating wheel and spring that set the rate of a mechanical watch: the portable answer to the pendulum.
Barrel
The toothed drum that houses a watch's coiled mainspring and delivers its torque to the gear train as the spring unwinds.
Bezel
The ring on the front of a watch case; fixed, it retains the glass, and on a divers' watch it turns to time a dive.
Bracelet
A watch band made of linked metal components, attached to the case at the lugs; ISO uses the same word for any watch band.
Case
The rigid outer housing that carries a watch's movement, dial and glass and, on a sealed watch, is what keeps water out.
Caseback
The closing panel on the back of a watch case, screwed or pressed into place, and sometimes made transparent to show the movement.
Chronograph
A watch that can record an elapsed interval: a function, not a precision rating. Constantly confused with chronometer.
Co-axial escapement
A detached escapement patented by George Daniels in 1979-80 that impulses the balance directly, put into series production by Omega from 1999.
Complication
Universally used, defined by no authority this Codex can cite. What was checked is recorded.
Crown
The knob outside a watch case, turned to wind the mainspring and set the hands, and on sealed watches screwed down against the case.
Detent escapement
The marine chronometer's escapement, in which a detent holds the escape wheel and the balance takes one impulse per complete oscillation.
Dial
The face of a watch: the plate carrying the markings against which the hands are read.
Dual time
A function showing a second time zone beside local time, usually on an extra hand; the dial word GMT is trade usage, not the timescale.
Eco-Drive
Citizen's own name for its light-powered quartz watches, which store converted light energy in a rechargeable cell rather than a battery.
Escape wheel
The toothed wheel at the end of a watch's train that the pallet fork locks and releases, passing the train's force on to the balance.
Escapement
The mechanism that lets the gear train advance in fixed steps while keeping the regulator oscillating. It is what makes a watch tick.
Gasket
The compressible ring or washer that seals a joint in a watch case; it is what makes a watch water-resistant, and it ages.
Gear train
The set of wheels carrying power from the mainspring to the escapement and the hands.
Guilloché
A repeating pattern cut into metal on a rose engine lathe, by hand or by machine; no body certifies which method produced a given pattern.
Hacking seconds
Trade term for a mechanism that stops the seconds hand when the crown is pulled out to set the time; no authority defines the term.
Hairspring
The fine spiral spring that returns the balance wheel and so fixes a mechanical watch's rate; spring and balance together form the oscillator.
Hand-winding
Winding a watch's mainspring by turning the crown, which drives the keyless works instead of a separate winding key.
Jewel
Synthetic hard stones used as bearings at points of wear. The number on a dial is a construction fact, not a quality score.
Keyless works
The crown-and-stem mechanism that both winds a watch and sets its hands, replacing the detachable key earlier watches needed.
Lever escapement
The escapement used in almost all mechanical watches, in which a pivoted lever locks and releases the escape wheel and impulses the balance.
Lift angle
The angle through which the escapement drives the balance; a figure a timing machine needs, for which no published standards definition was traced.
Lug
One of the projections from a watch case that hold the strap or bracelet; the gap between a facing pair is the lug width, quoted in millimetres.
Mainspring
The wound spring that powers a mechanical watch. It replaced the hanging weight and made portable timekeeping possible.
Mechanical watch
A watch powered by a wound spring and regulated by a moving mechanical oscillator, with no battery in the timekeeping path.
Minute repeater
A striking mechanism that sounds the time to the nearest minute only when the wearer operates it, instead of automatically at the hour.
Moon phase
A display of the Moon's phase, driven by a wheel whose tooth count only approximates the 29.53-day mean interval between new moons.
Pallet fork
The pivoted lever in a lever escapement whose two pallets lock and release the escape wheel and carry its impulse to the balance.
Perpetual calendar
A calendar mechanism that carries the date through months of unequal length and through the four-year leap cycle without needing to be reset.
Power reserve
In universal trade use, and defined by no standards or metrology body that publishes publicly. This entry records what was checked.
Quartz movement
Timekeeping by counting the vibrations of a quartz crystal, almost always at 32,768 Hz.
Radio-controlled watch
A quartz watch with a radio receiver that periodically resets itself from a national time-signal broadcast and keeps its own time in between.
Regulator (index)
An index that changes the active length of the hairspring, and so a watch's rate; the same word also names a separated-dial clock layout.
Rotor
The pivoted weight inside a self-winding watch that turns with the wearer's movement and winds the mainspring.
Shock-absorbing device
A sprung mounting for the balance staff's jewel bearings that lets the pivot move and re-centre under impact instead of breaking.
Silicon hairspring
A balance spring etched from silicon rather than drawn from metal alloy, made to be non-magnetic and dimensionally stable.
Skeletonised
A movement or dial whose plates have been cut away so the mechanism shows through; the British Museum catalogues such watches as skeletonised.
Spring Drive
Seiko's own name for a movement powered only by a mainspring but regulated electronically by a quartz oscillator instead of an escapement.
Strap
A watch band of leather, rubber or fabric, fastened to the case at the lugs; distinguished in trade use from a metal bracelet.
Thermocompensated quartz
A quartz movement that measures its own temperature and corrects the frequency error that temperature causes in the crystal.
Tourbillon
A rotating carriage that carries a watch's escapement and balance, turning them continuously instead of letting them rest in one position.
Tuning-fork watch
A watch whose oscillator is an electromagnetically driven tuning fork rather than a balance wheel; Bulova's Accutron is the known example.
World time
A display giving the time in every zone at once, read as a rotating 24-hour ring against a fixed ring of place names.
Units and measurement
Amplitude
The angular swing of a balance wheel away from its rest position, measured in degrees.
Atomic clock
A clock whose frequency is taken from an atomic transition; the caesium-133 transition is what defines the SI second.
Bar (pressure)
A non-SI unit of pressure equal to 0.1 megapascal, and the unit most often stamped on a watch's water-resistance marking.
Coordinated Universal Time
The world's reference time scale, produced by BIPM: the same rate as atomic time TAI, but offset from it by a whole number of seconds.
Daily rate
How many seconds a watch gains or loses in twenty-four hours, written with a sign, as in the range minus 4 to plus 6 seconds per day.
Gauss
A CGS unit of magnetic flux density, not an SI unit. 1 gauss = 10⁻⁴ tesla.
Hertz
The SI unit of frequency, equal to one cycle per second, used for the beat rate of a balance and for a quartz crystal's oscillation.
Isochronism
The property of an oscillator whose period does not change when the size of its swing changes.
Leap second
A one-second insertion into UTC that keeps civil time in step with the Earth's rotation; a watch has no way of knowing one happened.
Ligne
The traditional unit of movement diameter. Its metric value is quoted everywhere and could not be confirmed on a citable source.
Second
The SI base unit of time, defined since 2019 by fixing the caesium-133 hyperfine transition frequency.
Tesla
The SI unit of magnetic flux density; one tesla equals 10,000 gauss, the older unit watch specifications still use.
Vibrations per hour
The trade's unit for a mechanical beat rate: half-swings of the balance in an hour, counted two to each complete oscillation.
Trade and law
Assay office
The official body that tests articles of precious metal for fineness and strikes the hallmark, and whose own mark records which office did the work.
Counterfeit
In trade law, goods bearing without authorisation a trade mark identical to, or not distinguishable from, one validly registered for those goods.
Fineness
The proportion of precious metal in an alloy, written in parts per thousand: 750 for 18-karat gold.
Geographical indication
A sign used on products that have a specific geographical origin and possess qualities or a reputation due to that origin.
Hallmark
A mark struck on an article of precious metal by an official body to record the proportion of precious metal it contains.
In-house movement
A trade term for a movement a brand presents as its own design and production. No authority the Codex could find defines the threshold.
Manufacture
A trade word for a firm that makes its own movements. No law or standards body the Codex could find fixes what it requires.
Swiss made
A legally defined origin mark for watches, set by a Swiss federal ordinance that fixes where the development, movement, casing and costs must originate.
Materials
Crystal
The transparent cover over a watch dial, made of synthetic sapphire, mineral glass or acrylic.
Luminous material
The pigment applied to hands and dials so they can be read in the dark; the modern kind is a strontium aluminate that is charged by light.
Radium dial
A dial or set of hands painted with radium-based self-luminous paint, used until about 1970; such items remain radioactive.
The honest column
Where the record is open
33 of these 80 entries could not be closed from a citable source. They are listed here rather than left to be discovered, and each one names what was checked and the document that would close it. The two lists mean different things.
No authority defines the term (15)
In universal trade use, and no standards body, metrology institute, museum or law that this Codex could open has fixed the meaning.
- Power reserve
- Ligne
- Complication
- Vibrations per hour
- Case
- Dial
- Caseback
- Gasket
- Bracelet
- Strap
- Lift angle
- Hacking seconds
- Skeletonised
- Manufacture
- In-house movement
An authority exists, but part of the answer is not public (18)
The issuing body is identified and quoted as far as its published material goes; the rest sits in a text that is not public, so it is not quoted or guessed at.