How Watches Work
In addition to their exterior beauty, watches are also an incredible feat of engineering and craftsmanship. This section contains an overview of the major parts of a watch, as well as an explanation of how watches operate. Many complicated parts must all work in tandem in order to not only tell time, but perform a myriad of other functions. These could include a chronograph, altimeter, alarm, day/date calendar, moon phase, and slide rule bezel. Below are descriptions of the major internal and external parts and their functions.
External Watch Parts
The crystal is the cover over the watch face. Three types of crystals are commonly found in watches. Acrylic crystal is an inexpensive plastic that allows shallow scratches to be buffed out. Mineral crystal is composed of several elements that are heat-treated to create an unusual hardness that aids in resisting scratches. Sapphire crystal is the most expensive and durable, approximately three times harder than mineral crystals, and 20 times harder than acrylic crystals.
A watch’s hands are the pointing devices anchored at the center and circling around the dial, indicating hours, minutes, seconds, and any other special features of the watch. There are many different types of hands.
Alpha: A hand that is slightly tapered
Baton: A narrow hand, sometimes referred to as a ‘stick hand’
Dauphine: A wide, tapered hand with a facet at the center, running the length of the hand
Skeleton: Cutout hands showing only the frame
Luminous: Hand-made of skeleton form, the opening filled with a luminous material
The bezel is the surface ring on a watch that surrounds and holds the crystal in place. A rotating ratchet bezel moves in some sport watches as part of the timing device. If rotating bezels are bi-directional (able to move clockwise or counter clockwise), they can assist in calculations for elapsed times.
The crown is the nodule extending from the watch case that is used to set the time, date, etc. Most pull out to set the time. Many water-resistant watches have crowns that screw down for a better water-tight seal.
The dial is the watch face that contains the numerals, indices, or surface design. While these parts are usually applied, some may be printed on. Sub-dials are smaller dials set into the main face of the watch. These can be used for added functions, such as elapsed times and dates.
The watch case is the metal housing that contains the internal parts of a watch. Stainless steel is the most typical metal used, but titanium, gold, silver and platinum are also used. Less expensive watches are usually made of brass that has been plated with gold or silver.
A bracelet is the flexible metal band consisting of assembled links, usually in the same style as the watch case. Detachable links are used to change the length of the bracelet. Bracelets can be made of stainless steel, sterling silver, gold, or a combination.
A strap is simply a watchband made of leather, plastic, or fabric.
Internal Watch Parts
A watch’s movement is its main timekeeping mechanism. Today’s watch movements fall into two categories, automatic mechanical or quartz. Automatic mechanical movements mark the passage of time by a series of gear mechanisms. Most automatic movements are wound by the normal, everyday movement of your wrist, which charges the watch’s winding reserve. Quartz movements are powered by a battery and do not stop working once removed from your wrist.
The balance wheel is the regulating organ of a watch with a mechanical movement that vibrates on a spiral hairspring. Lengthening or shortening the balance spring makes the balance wheel go faster or slower to advance or retard the watch. The travel of the balance wheel from one extreme to the other and back again is called oscillation.
This series of small gears in both quartz and mechanical movement watches is responsible for transmitting the power from the battery (in a quartz watch) or spring (in a mechanical watch) to the escapement, which distributes the impulses that mark the time.
A tourbillon, which means “whirlwind” in French, is an addition to the mechanics of a watch escapement. It mounts the escapement and balance wheel in a rotating cage to negate the effect of gravity when the timepiece (and thus the escapement) is stuck in a certain position.
This part of the watch restricts the electrical or mechanical impulses of the gear train, metering out the passage of time into equal, regular parts.
The motion work is a series of parts inside a watch that receive power from the escapement and gear train, which distribute and generate the watch’s power. The motion work is responsible for actually turning the watch’s hands.
The mainspring is the energy source responsible for powering the watch movement (as opposed to a battery in a watch with a quartz crystal movement). The spring is wound, either manually (using the winding stem) or automatically, by the motion of the wearer’s wrist. Potential energy is stored in the coiled spring, then released to the gear train which transmits the power to the escapement and motion work, which turns the hands on the watch dial.
Putting it all together
Watches essentially tell time by the integration of three main components, an energy source, a time regulating mechanism, and a display. The energy source can be electronic (as in a battery) or mechanical (as in a wound spring). A watch’s main timekeeping mechanism is called its movement. Today’s watches fall into two categories, mechanical movements and quartz movements. Here’s a breakdown of how each type of movement works: