The transmission system or geartrain transmits the energy stored in the barrel to the escape-wheel.
- The first wheel after the barrel is the centre-wheel. As its name indicates, it lies at the heart of the movement. This wheel performs 1 full turn in 12 hours , and it carries the hour hand.
- The next wheel, called the third wheel, is an intermediate wheel.
- The next wheel is called the fourth wheel. This wheel may also be positioned at the centre of the movement, or located at 6 o'clock on the dial. It performs 1 full turn in 1 minute or 60 seconds (which is why it is also referred to as a seconds wheel) and serves to carry the seconds hand on watches equipped with such a hand.
These three wheels are in brass.
- The final wheel is the escape wheel. It is not part of the gear train but the escapement. It releases the energy transmitted via the gear train to the pallet-lever in an intermittent manner.
This wheel is very different from the three others. It is made of a special, highly resistant steel and undergoes an amazing number of shocks when hitting the pallet-lever (an average of 21,600 impacts in one hour or. 518,000 in 24 hours).
The form of the teeth is also very different. This wheel is one of the most difficult and delicate movement parts to make.
- Dial side: the cannon pinion that carries the minute hand slides over the shaft of the centre wheel. It drives the minute wheel that carries the minute pinion, which in turn drives the hour wheel.