The Wheel Train
The wheel train changes the speed of the barrel, one revolution in 7 hours, to the escape wheel’s one revolution in 5 seconds!
The Mainspring Barrel circumference (first wheel to the left) has teeth that are connected to the next pinion in the wheel train. The rotation of the barrel is accelerated in 4 steps, including the escape wheel pinion. As can be seen in the figure the first wheel after the barrel is the center wheel, also called the 2nd wheel. The name is given because that this wheel, in almost all cases, is in the very center of the movement aligned to the arbor of the watch hands. As a matter of fact this wheel has a rotational speed of one revolution in an hour, and hence the minute hand is attached to its arbor.
The speed is further increased via the third wheel to the fourth wheel, which makes one revolution per minute and has the second hand attached to its arbor. Finally the fourth wheel engages the escape wheel pinion.
Third Wheel (210)
Fourth Wheel (224)
Escape Wheel (705)