Compared to electronic movements, mechanical stopwatches are less accurate, often with errors of seconds per day, and they are sensitive to position, temperature[9] and magnetism.[10] They are also costly to produce, require regular maintenance and adjustment, and are more prone to failure. Nevertheless, the craftsmanship of mechanical stopwatches still attracts interest from part of the stopwatch-buying public. Skeleton stopwatches are designed to leave the mechanism visible for aesthetic purposes.
Mechanical movements use an escapement mechanism to control and limit the unwinding and winding parts of a spring, converting what would otherwise be a simple unwinding into a controlled and periodic energy release. Mechanical movements also use a balance wheel together with the balance spring (also known as a hairspring) to control motion of the gear system of the stopwatch in a manner analogous to the pendulum of a pendulum clock. The tourbillon, an optional part for mechanical movements, is a rotating frame for the escapement, which is used to cancel out or reduce the effects of gravitational bias to the timekeeping. Due to the complexity of designing a tourbillon, they are very expensive, and only found in "prestige" stopwatches.
The pin-lever escapement (called the Roskopf movement after its inventor, Georges Frederic Roskopf), which is a cheaper version of the fully levered movement, was manufactured in huge quantities by many Swiss manufacturers as well as Timex, until it was replaced by quartz movements.[11][12][13]
Tuning-fork stopwatches use a type of electromechanical movement. Introduced by Bulova in 1960, they use a tuning fork with a precise frequency (most often 360 hertz) to drive a mechanical stopwatch. The task of converting electronically pulsed fork vibration into rotary movement is done via two tiny jeweled fingers, called pawls. Tuning-fork stopwatches were rendered obsolete when electronic quartz stopwatches were developed. Quartz stopwatches were cheaper to produce and even more accurate.
Main article: Mainspring
Traditional online stopwatch movements use a spiral spring called a mainspring as a power source. In manual stopwatches the spring must be rewound periodically by the user by turning the stopwatch crown. Antique pocketstopwatches were wound by inserting a separate key into a hole in the back of the stopwatch and turning it. Most modern stopwatches are designed to run 40 hours on a winding and thus must be wound daily, but some run for several days and a few have 192-hour mainsprings and are wound weekly.
Automatic stopwatches
Main article: Automatic stopwatch
Automatic stopwatch: An eccentric weight, called a rotor, swings with the movement of the wearer's body and winds the spring
A self-winding or automatic stopwatch is one that rewinds the mainspring of a mechanical movement by the natural motions of the wearer's body. The first self-winding mechanism was invented for pocket stopwatches in 1770 by Abraham-Louis Perrelet,[14] but the first "self-winding", or "automatic", wriststopwatch was the invention of a British stopwatch repairer named John Harwood in 1923. This type of stopwatch allows for constant winding without special action from the wearer; it works by an eccentric weight, called a winding rotor, which rotates with the movement of the wearer's wrist. The back-and-forth motion of the winding rotor couples to a ratchet to automatically wind the mainspring. Self-winding stopwatches usually can also be wound manually so they can be kept running when not worn or if the wearer's wrist motions are inadequate to keep the stopwatch wound.