Though construction of different models may vary, all mechanical watches tend to have five fundamental parts.
Mainspring is a spiral ribbon inside a cylindrical barrel that stores the mechanical energy of the watches and keeps the gear train moving. Once an hour the gear teeth outside the barrel turn the center wheel and its shaft that goes through the dial. The minute hand is driven by the reduction gearing that turns the hour wheel and hand once for every 12 revolutions of the minute hand.
A gear train takes the energy from the mainspring and pushes the balance wheel. The center wheel drives the pinion of the third wheel, the third wheel drives the pinion of the fourth wheel and so on.
The weighted wheel that goes back and forth, making each swing precisely the same amount of time. This is the main timekeeping element in the watch. Most balance wheels oscillate at 5, 6, 8, or 10 beats per second. This translates into 2.5, 3, 4, and 5 Hz respectively, or 18000, 21,600, 28,800, and 36,000 vibrations per hour.
An escapement mechanism pushes the balance wheel of the lever escapement and makes it advance by the set amount at a time. It forces the gear train to make periodic stops and produce that distinctive ticking sound. As the escape wheel turns, its tooth pushes against the lever, which gives the balance wheel a brief push, keeping it swinging back and forth.
The front side of watches where user can get all the time information. Hour, minute and second hands, numerical scales and most of the complications such as calendar or power reserve indicator are displayed here.