The very fine, delicately coiled wire at the heart of a mechanical watch movement. It sits on a balance wheel (the oscillating wheel you can see when you look through the back of a watch with a see-through case back) and is almost invisible to the naked eye when the wheel is in motion.

The metal pin system that secures a strap to the wrist.

The words calibre and movement are often used interchangeably. Both refer to the assortment of small parts that combine to create a mechanism that can turn power stored in a barrel into an accurate timing device. Purely, calibre refers to a particular movement designation.

The back of a watch. Usually but not always made of the same material as the case and sometimes with a see-through plate so the movement is visible. This is sometimes known as an exhibition case back.

A central hand, usually thinner than the hour and minute hands, that shows the running seconds of a watch. Chronographs usually have central seconds hands to show the time recorded by the chronograph function. See also Small seconds.

Diver's watches have to perform a number of functions impeccably - it could be a matter of life or death. One of those is to accurately and reliably relay dive time. This is done by aligning the bezel's zero marker with a watch's minute hand and then reading off elapsed dive time. In a proper diver's watch, the bezel will rotate only in an anti-clockwise direction, so that the time indicated can never be accidentally shortened, thus suggesting to a diver they have more oxygen remaining than they do.

ISO 6425 lays out a full definition of a diver's watch, the headlines being water resistance of at least 100m, a uni-directional rotating bezel, running seconds and legibility at 25cm in the dark.

Diamond-like carbon - a carbon coating, often black, applied to watch cases. DLC is generally superior to PVD. See also PVD.

Top watch companies employ dozens of skilled craftspeople whose job it is to finish watch parts - cases, bridges, hands, etc. These finishes are often highly detailed. Finishing is one of the qualities that separates a luxury watch from the rest.

One of the big third-party movement manufacturers. Owned by Swatch Group, parent company of Omega, Longines and Tissot, it also produces movements for dozens of other Swiss brands.

A chronograph with a seconds had that can be reset to zero and restarted with a single push of a button.

Found on some advanced diver's watches and only useful to saturation divers who spend time in pressurised, helium-rich environments. Helium particles are smaller than air and can penetrate a watch case during compression dives. During decompression, these particles expand and could damage a watch unless released through a helium escape valve. Some of these valves are automatic; some have to be operated manually.

A term used to describe a watch or movement developed, produced and assembled by the same company whose name appears on the dial. Very few dial names can claim to create every part of a watch movement. Historically, the industry was a series of specialist producers who supplied établisseurs, or assemblers, who then put a name on the dial for retail. The verticalisation of watch manufacturing is a relatively modern phenomenon that has come to carry great kudos.

A softer, less scratch-resistant glass than sapphire crystal, sometimes used in case backs.

A watch with a high-end complication that can chime the time on demand.

A chronograph that's started, stopped and reset using a single pusher, sometimes secreted into the crown.

A watch with a display showing the phases of the moon during its 29.5-day cycle.

The name given to the assortment of parts that combine to create a unit that can keep track of time, loosely defined as the winding and hand-setting mechanism, the mainspring, the gears, the escapement and the regulating organ.

Term given to chronographs that have white dials with black or grey subdials. Where the dial is black and the subdials white, the term reverse panda is used.

Quartz movements use a battery-powered system of electronics to keep track of time. Typically, quartz movements are cheaper and more accurate than their mechanical equivalents, but also considered less romantic. In the 1960s and 1970s, when the technology was new, quartz, although initially expensive, became hugely popular. The mechanical-watch industry suffered in what became known as the Quartz Crisis. In Switzerland, about 1,000 watch businesses went bust and two-thirds of the workforce were laid off. The current preoccupation with mechanical watches began in the late 1980s and has gathered pace ever since.

One of the big third-party movement manufacturers and ETA's great rival. Like ETA, most of its exports are reliable, tried-and-tested movements. They just don't carry the kudos of an in-house calibre. See also ETA.

Manufacturers recommend you get a new mechanical watch serviced every three to five years, and a vintage watch every two years. A service involves stripping a watch down and cleaning and relubricating it so that it maintains its accuracy. Servicing a luxury watch can cost hundreds of pounds, rising as the watch becomes more complicated. Worth factoring in when making a purchase.

Over the past 10 to 15 years, watch brands have introduced silicon into watchmaking, particularly into the balance. Silicon is watchmaking wonderstuff because it's resistant to perilous things such as shock, magnetism and changes in temperature and because it requires very little maintenance.

A skeletonised watch has no dial. Instead, the watchmaker hollows out and decorates the movement so it can be seen in all its glory, creating an intricate, arcane look that many watch collectors go crazy for.

A subdial that shows the running seconds.