The gear train has two main functions in a mechanical watch: to transmit energy from the mainspring barrel to the rest of the movement and to display the time.

The Transmission

This essential component ensures the proper transmission of energy from the mainspring barrel to the escape wheel. This is why the gear train is also referred to as the transmission system. To achieve this, the gear train receives energy from the mainspring barrel via the gearing of the upper part of the barrel, and in turn, transmits it to the escapement through the movement of the wheels. The energy generated by the gear train is regulated by the balance wheel, another essential component of any mechanical watch.

The Display

The display of time on a mechanical watch would not be possible without gear trains. The toothed wheels and pinion wheels that make up the gear trains enable the hour, minute, and second hands to turn. This is why there are generally three wheels in a mechanical watch: one for the hour, one for the minutes, and one for the seconds. Each of these wheels will therefore have a different size and number of teeth to ensure rotation in sync with time. Other gear trains are found in complication watches. These allow for the integration and display of the date, moon phases, etc.