How does an automatic mechanical watch work?

　　An automatic mechanical watch is based on the structure of a standard mechanical watch, with the addition of an automatic winding mechanism that automatically winds the mainspring through the motion of the wearer's arm during daily wear. The dial is printed with the words "Automatic" to indicate that it is an automatic mechanical watch, which can be further classified into fully automatic and semi-automatic mechanical watches.

　　To understand the principle of an automatic mechanical watch, one needs to understand its automatic mechanism. The automatic mechanism achieves the special function of automatic winding through the oscillation of a weight (automatic rotor), which is connected to the mainspring system via the automatic winding wheel train.

　　Difference between semi-automatic and fully automatic principles in automatic mechanical watches: The driving component of an automatic watch is the weight (i.e. automatic rotor), which winds the mainspring automatically through the movement of the arm via a set of automatic wheel trains acting as the automatic winding transmission system. Due to the different working states of the weights and automatic winding systems used in automatic watches, the structure of automatic mechanical watches can be divided into the following four types:

　　1. Oscillating unidirectional winding;

　　2. Oscillating bidirectional winding;

　　3. Rotational unidirectional winding,

　　4. Rotational bidirectional winding;

　　An oscillating automatic weight can only swing by about 120° within the watch movement, which is semi-automatic. A rotational automatic weight can rotate by 360° within the movement, which is called fully automatic. These are the principles of semi-automatic and fully automatic mechanical watches.

　　Some early automatic mechanical watches featured a bumper winding system where a weighted mass moved back and forth in a straight line within two grooves across the centre of the movement; this winding mechanism was known as a bumper automatic. Due to its poor winding efficiency, it was long ago phased out. However, because of its limited production numbers, it holds considerable collectable value.

　　Certain automatic mechanical watches feature a hand on the dial to indicate the remaining power reserve, allowing you to gauge the reliability of the automatic winding. Due to its complex mechanism, which requires 14 components, very few automatic watches adopt this type of complication.