Glossary
The terms that appear on the spec sheets, explained in a sentence or two. Each links to its guide where there is one.
- Automatic
- A mechanical watch that winds itself as your wrist moves: a half-moon rotor spins as you move and tightens the mainspring. If you don’t wear it, it stops once the power reserve runs out.
- Calibre
- The mechanism that drives the watch. Each maker numbers its own (4R36, Powermatic 80, F6922), and that number tells you more about the watch than the name on the dial. Read more
- Power reserve
- How many hours the watch keeps running once you take it off. With 40 hours it lasts a night and a day; with 80, a whole weekend. Read more
- Beat rate (bph)
- The balance wheel’s beats per hour. At 21,600 bph the seconds hand makes 6 steps a second; at 28,800, 8. A higher rate tends to be more stable but does not guarantee better accuracy. Read more
- Jewels
- Synthetic stones at the pivots of the movement that reduce friction. A normal automatic has between 21 and 26; more jewels do not make a better watch.
- Crystal
- The transparent cover over the dial. Sapphire barely scratches; Seiko’s Hardlex and mineral glass scratch sooner but chip less and cost less to replace. Read more
- Water resistance
- The water pressure the case withstands in a laboratory test. 30 m copes with rain; 100 m with swimming; 200 m with ISO 6425, with diving. Read more
- Hacking seconds
- When you pull out the crown, the seconds hand stops so you can set the watch to the second. The most basic movements lack it. Read more
- Hand winding
- Being able to wind the watch by turning the crown, to get it going without shaking it. Read more
- Lug-to-lug
- The distance from the tip of one pair of lugs to the other, where the strap attaches. It is the measurement that decides whether a watch fits your wrist, more than the diameter. Read more
- Diameter
- The width of the case without the crown. It gives an idea of size, but two watches with the same diameter can wear very differently depending on lug-to-lug and thickness.
- Rotating bezel
- The ring around the crystal. On dive watches it turns one way only to time a dive; on GMT watches it turns both ways to read another time zone.
- GMT
- An extra hand that goes round once every 24 hours and, with the bezel, shows the time in a second time zone.
- ISO 6425
- The international standard for dive watches: it requires tested water resistance, a unidirectional bezel, legibility in the dark and resistance to shocks and magnetism.
- Display caseback
- A transparent back that shows the movement and the rotor turning.