Caliber

A caliber is a particular movement design, identified by its maker and a reference number. Two watches from different brands can share a caliber, and one brand can use a dozen across its range, so it is the most precise way to say what is actually inside a watch. The spellings caliber and calibre both mean the same thing.

Historically the term referred to the layout and size of a movement rather than a model. Size was quoted in lignes, an old French unit of about 2.2558 mm, and a specification sheet may still give a movement's diameter that way alongside millimeters. That explains odd-looking numbers: 11 and a half lignes is 25.60 mm.

How to read the spec

A caliber designation is a lookup key. Once you have it, a manufacturer's technical documentation will give you diameter, height, jewel count, frequency, power reserve, the functions supported and the regulation grade offered. That last point matters: many ébauche calibers are sold in several grades, so two watches listing the same movement can be adjusted to noticeably different standards.

Three calibers cover most of what you meet in a Swiss mechanical watch.

The Sellita matches the ETA to two decimal places, which is why it drops into cases built for the older caliber. Our comparison of the two covers where they actually differ.

Grades, and what they are worth

Grade is the part of a specification buyers skip and watchmakers read first. ETA sells the 2824-2 in four executions, Standard, Elabore, Top and Chronometre, differing in hairspring, balance, pallet stones, mainspring and shock protection, but publishes no daily rate for each grade. Sellita does. Its 2017 data sheet gives Standard at plus or minus 12 seconds a day, Special (Elabore) at 7, Premium (Top) at 4, and Chronometre to COSC criteria, with the caveat that those limits are met by 95 percent of a delivered lot, not by every movement. A listing naming only the caliber has given you the architecture and withheld the number that decides how the watch runs.

Base calibers and modifications

Movements are also modified. A base caliber supplies the going train and escapement, and a module or a set of reworked parts adds functions or changes the finish, which is why specifications say things like "based on the Sellita SW200-1".

Brands also rename what they buy, so a number in a brand's own series does not mean the brand designed the movement: TAG Heuer's Calibre 16 is a 7750-based chronograph. Telling a renamed base from a genuinely in-house design is the subject of our in-house versus third-party comparison.

Where you find the number

Behind a solid caseback the caliber is usually only on paper: the specification page, the warranty booklet or the maker's site. Through an exhibition caseback it is often engraved on the rotor or a bridge, and on a bare movement it is stamped on the mainplate under the dial, which is how a watchmaker identifies one in seconds. Reading a specification properly means treating a missing caliber as information: a brand that lists "automatic movement" and nothing else has made a choice, and secondhand that is worth a question.

Why it matters

The caliber tells you what servicing will involve, whether parts are widely available, and how well understood the movement is by independent watchmakers. A widely used workhorse such as the ETA 2824-2, its Sellita counterpart or the ETA 7750 chronograph can be serviced almost anywhere. A proprietary in-house caliber may perform superbly and still tie you to the maker's service network for parts, which is a real ownership cost. As indicative US figures before sales tax, a full service on a three-hand automatic runs roughly $250 to $500 with an independent and $350 to $600 at a brand service center; see our service costs.

Terms it gets confused with

A caliber is a design; a movement is the physical object built to it. A manufacture is a company that makes movements rather than a movement itself, and an ébauche is an unfinished movement sold on for someone else to finish, jewel and regulate.