ABCs of Watchmaking

If you ever took a watch apart to admire the graceful dance of its movement and wondered what does it take to bring this beautiful piece of machinery to life, then this guide could be a fine starting point to quench your watch enthusiasm. Here, we spell out – quite literally – all the most crucial terms in watchmaking, like balance wheel, hairspring, caliber and jewels (the latter aren't at all what they sound like and carry important functions beyond aesthetics).

Amplitude

Measured in degrees of rotation, one oscillation – or swing – of the balance wheel. This unit of measurement can be used to gauge the health of the watch in relationship to service intervals.

Balance Wheel

The part of a mechanical watch movement that oscillates (a.k.a. rotates back and forth) with regulation from the balance spring. Also known as the regulating organ (in combination with the hairspring), each swing of the balance advances the pallet fork (in most cases) and unlocks and locks the escape wheel, which then unwinds the mainspring at a controlled rate.

Caliber

A designation for the specific model or type of a watch's movement – often a shorthand reference to the watch's design and mechanics. A small change to an existing caliber will change the caliber number – e.g. 3230 (no-date Rolex automatic movement) vs. 3235 (Rolex automatic with date). Also, even a slight modification (or not) of a Manufacture's movement can be renamed as an entirely different brand's caliber (i.e. AP’s 2120 which is based on the JLC 920).

Dual Time

A watch that displays two different time zones at once, with the ability to adjust each one separately. Sometimes harnessing two separate movements or one movement with the ability to track and adjust two time zones (this can be identified by the number of crowns like in this Cartier ref. W1502853).

Escapement

The escapement (in most cases, the Lever escapement) is made up of several parts and is impulsed by the regulating organ (balance wheel and hairspring). They work together to unwind the mainspring at a controlled rate and rely on the ratios of wheel and pinion teeth to translate the time via rotating hands on a watch’s dial.

Frequency

The frequency of a watch is measured in Hertz (Hz) and/or vibrations per hour (vph). A vibration is half of an oscillation. E.g. a watch with 18,000 vph (or 2.5 Hz) vibrates 5 times in a second (18,000/60 = 300. 300/60 = 5). So, Hz is equal to vibrations per second divided by two, and this figure dictates how smooth the sweeping seconds hand is on a watch with a conventional escapement.

Guilloché

Engine turning (or Guilloché) is a traditional hand-turned process engraving repeated straight-line or geometric patterns into a dial plate. Using a mechanical rose engine or ‘decorative lathe with a series of indexing plates, patterns can be precisely engraved into these metals creating one of the most beautiful – and difficult – decorations in dial-making.

Hairspring

A tiny coil spring inside the balance wheel of mechanical watches. It's responsible for keeping the balance wheel oscillating at a consistent frequency, which helps it keep time accurately. It’s also known as the balance spring.

Jewels

Synthetic rubies or sapphires, used as bearings within a watch movement to minimize friction and deter wear and tear.

Lugs

The case extensions that hold a strap or bracelet in place.

Openworked

Not to be mistaken with skeletonizing, it’s a technique that exposes the inner workings of a watch's movement. This involves reducing the size of the dial or removing it altogether, as well as hollowing out the plates, bridges, and other parts to expose the watch’s gears, balance wheel, and more parts.

Power Reserve

The amount of time it takes the movement of a watch to run out of energy after it has been fully wound, without being rewound by hand (for manual watches) or self-wound (for automatic watches).

Radium

A radioactive material once used in luminescent paint on watch dials and hands to make them glow in the dark. It's now been replaced by safer alternatives.