Mechanical watch

A device called an escapement releases the watch's wheels to move forward a small amount with each swing of the balance wheel, moving the watch's hands forward at a constant rate.

[2] The internal mechanism of a watch, excluding the face and hands, is called the movement.

If the movement is dirty or worn, the power may not transfer from the mainspring efficiently to the escapement.

The other end of the lever has a fork which engages with an upright impulse pin on the balance wheel shaft.

A balance wheel's period of oscillation T in seconds, the time required for one complete cycle (two beats), is where

Moving the regulator lever slides the curb pins up or down the spring to control its effective length.

A separate set of gears called the keyless work winds the mainspring when the crown is rotated, and when the crown is pulled out a short distance allow the hands to be turned to set the watch.

The stem attached to the crown has a gear called the clutch or castle wheel, with two rings of teeth that project axially from the ends.

A spring-loaded pawl or click presses against the ratchet teeth, preventing the mainspring from unwinding.

When the crown is turned, the friction coupling of the cannon pinion allows the hands to be rotated.

Any fluttering due to the indirect gearing is concealed by the relatively slow movement of the minute hand.

This redesign brought all the train gearing between the plates and allowed a thinner movement.

[12] Jewel bearings were invented and introduced in watches by Nicolas Fatio (or Facio) de Duillier and Pierre and Jacob Debaufre around 1702[13][14] to reduce friction.

[13] In 1902, a process to grow artificial sapphire crystals was invented, making jewels much cheaper.

Jewels in modern watches are all synthetic sapphire or (usually) ruby, made of corundum (Al2O3), one of the hardest substances known.

[15] The advantage of using jewels is that their ultrahard slick surface has a lower coefficient of friction with metal.

In unjeweled bearings, the pivots of the watch's wheels rotate in holes in the plates supporting the movement.

The sideways force applied by the driving gear causes more pressure and friction on one side of the hole.

In some of the wheels, the rotating shaft can wear away the hole until it is oval shaped, eventually causing the gear to jam, stopping the watch.

Friction has the greatest effect in the wheels that move the fastest, so they benefit most from jewelling.

[18] In quality watches, to minimize positional error, capstones were added to the lever and escape wheel bearings, making 21 jewels.

When self-winding watches were introduced in the 1950s, several wheels in the automatic winding mechanism were jeweled, increasing the count to 25–27.

However, by the early 20th century watch movements had been standardized to the point that there was little difference between their mechanisms, besides quality of workmanship.

Although initially this was a good measure of quality, it gave manufacturers an incentive to increase the jewel count.

[23] In 1974, the International Organization for Standardization (ISO) in collaboration with the Swiss watch industry standards organization Normes de l'Industrie Horlogère Suisse (NIHS) published a standard, ISO 1112, which prohibited manufacturers from including such nonfunctional jewels in the jewel counts in advertising and sales literature.

There are usually 27 cities (corresponding to 24 major time zones) on the city bezel, starting with GMT/UTC: Peter Henlein has often been described as the inventor of the first pocket watch, the "Nuremberg egg", in 1510, but this claim appears to be a 19th-century invention and does not appear in older sources.

Early watches were terribly imprecise; a good one could vary as much as 15 minutes in a day.

Modern precision (a few seconds per day) was not attained by any watch until 1760, when John Harrison created his marine chronometers.

Industrialization of the movement manufacturing process by the Waltham Watch Company in 1854 made additional precision possible; the company won a gold medal at the 1876 Philadelphia Centennial Exposition for their manufacturing quality.

Modern mechanical watches require of the order of 1 microwatt of power on average[26] Because the mainspring provides an uneven source of power (its torque steadily decreases as the spring unwinds), watches from the early 16th century to the early 19th century featured a chain-driven fusee which served to regulate the torque output of the mainspring throughout its winding.