Watch Glossary

The terms and acronyms you will see everywhere — defined once, clearly.

ATM (Atmosphere): A unit of pressure measurement used for water resistance. 1 ATM is roughly equal to 10 meters of depth, but the rating is derived from static pressure tests, not actual diving.

Automatic: A mechanical movement that winds itself via a swinging rotor driven by the motion of the wrist. The modern standard for mechanical watches.

Beat rate: The frequency at which a movement is oscillator swings, measured in vibrations per hour (vph) or hertz (Hz). See also: vph.

Bezel: The ring surrounding the watch crystal. Can be fixed (decorative) or rotating (functional, as on dive watches).

Brushed finish: A matte textured finish on metal surfaces, achieved by brushing with an abrasive. Tool watches typically have brushed cases to hide scratches.

BPH / VPH: Beats per hour / vibrations per hour. The frequency of a mechanical movement. Standard rates are 21,600, 28,800, and 36,000 vph.

Diver is 200M: A labeling standard indicating the watch is suitable for scuba diving, per ISO 6425 requirements. Look for this designation rather than just a depth rating.

DLC (Diamond-Like Carbon): A hard coating applied to metal watch components for scratch resistance and visual effect. More durable than standard PVD coating.

Dress watch: A relatively thin, refined watch intended for formal or business settings. Typically smaller case diameter, simpler dial, leather strap.

ETA: The former premier supplier of Swiss mechanical movements. Now part of Swatch Group and heavily restricted in external sales. Most microbrands use Sellita as the alternative.

Exhibition caseback: A display window on the caseback, usually made of sapphire, allowing the wearer to view the movement.

GMT: Greenwich Mean Time, and by extension a watch function that displays a second time zone. Two types exist: office GMT (24-hour hand set to home time) and traveler GMT (independently jumping local hour hand).

Guilloche: Engine-turned decorative pattern cut into a dial surface. Creates geometric or wave patterns that catch light distinctly.

Lug-to-lug: The distance between the outermost points of the case, measured through the center. Determines how the watch spans the wrist and whether it will fit under a shirt cuff.

Lume: Short for luminous material, applied to hands and indices for readability in low-light conditions. Modern standard is Super-LumiNova.

Microbrand: An independent watch brand, typically small in scale, that uses third-party movements and focuses on design, value, and community rather than manufacturing scale.

Moonphase: A complication that displays the current phase of the moon on a sub-dial. Romantic and traditional; accuracy varies from 122 years to 577 years before requiring correction.

Movement: The internal mechanism of a watch. See also: caliber.

Miyota: A Japanese movement manufacturer owned by Citizen. The 8215 and 9015 are among the most common calibers in affordable microbrand watches.

PVD (Physical Vapor Deposition): A thin coating applied to metal for color, hardness, and corrosion resistance. Used for black, gold, and other colored watch surfaces.

Polished finish: A mirror-like reflective surface achieved by buffing. On tool watches, polished surfaces show scratches more readily than brushed surfaces.

Rolex clap: A bracelet clasp named after its inventor, named for Rolex is extensive use. Characterized by a thin profile and flip-lock folding mechanism. Also used by many other brands.

Sapphire crystal: A synthetic sapphire cover, extremely scratch-resistant (Mohs 9). The premium choice for watch crystals.

Screw-down crown: A crown that screws into the case to create a watertight seal. Standard on most dive watches.

Sellita: A Swiss movement manufacturer that became critical to the microbrand market after ETA restricted supply. Makes the SW200 and SW300 as alternatives to ETA 2824 and 2892.

Super-LumiNova: The most common photoluminescent compound used in modern watches. Available in different grades; higher grades glow brighter and longer.

Tool watch: A watch designed for a specific purpose — diving, piloting, mountaineering — rather than pure aesthetics. Typically has corresponding functional features.

Tourbillon: A rotating cage mechanism in a mechanical movement, invented to counteract the effects of gravity. Considered a high-end complication. Expensive to produce and service.

VPH: Vibrations per hour. The beat rate of a mechanical movement. Higher is generally smoother; 28,800 is the modern standard.

In-house: A movement or component designed and manufactured by the brand itself, rather than purchased from an external supplier. Carries prestige but does not automatically mean superior quality.

Manufacture: In French, the is term is manufactures. In watchmaking, it implies the brand controls its own production including movement manufacturing. Used loosely for brands that make some but not all of their components.

Modular movement: A movement designed to accept add-on complications (like a chronograph module) without redesigning the base caliber. ETA is known for modular architecture.

Standard movement: A mass-produced movement bought from a supplier like Miyota, Seiko, or Sellita, then customized with decoration or regulation by the brand.