first wheel. The first wheel (closest to the cam) is said to be picked up when this occurs. As this first wheel rotates, its drive pin will in turn engage the fly on the second wheel and the second wheel will begin rotating with the dial and the closest wheel in a similar fashion. Once all wheels are "picked up" and rotating together with the dial, the dial is rotated until the first position/number of the combination is indicated, which means the wheel furthest from the cam is in place and its gate is aligned under the fence. The number of wheels also determines the number of rotations past the first position required to reset the lock; since picking up all the wheels requires a number of rotations equal to the number of wheels, the final wheel (furthest from the cam) cannot be not picked up and positioned until the minimum number of rotations is completed. After the furthest wheel is positioned, by reversing the rotation of the dial, all the drive pins and flys disengage; as the dial continues to rotate in the opposite direction, the cam will again "pick up" the wheels in sequence (starting from the first wheel, closest to the cam) until all the wheels (save the wheel furthest from the cam) rotate together. In this way, the remaining wheels are rotated without disturbing the alignment of the furthest wheel. Once the second position/number is indicated, the next-to-furthest wheel is in place and its gate is properly aligned with the fence. The rotation of the dial is then reversed again until the remaining wheels are picked up and the gate of the next wheel is aligned with the fence. In this way, by turning the dial back and forth to the correct sequence of positions, all the wheels will be aligned with their gates positioned under the fence. Once the gates are aligned on all the wheels, the fence drops into the gates, allowing the nose of the lever to engage with a corresponding gate in the cam. Further rotation of the dial moves the lever, retracting the locking mechanism and opening the lock. Wheel sandwich construction Wheels are typically made of a three-layer sandwich. The outer layers, known as the wheel case, contain the gate and surround the externally-toothed wheel center, change key cam, and lever arms. When a change key is inserted into the