This view from the back of the machine shows the slotted comb and the extended rotor teeth that form the quick-clearing mechanism.

The comb is able to slide a short distance along the back plate. It is coupled to the handle locking shaft (via the pin visible in the opening at the bottom left), and moves in tandem with the rotor locking bar.

During a normal cycle, the handle locking shaft is in its outer position (to the left in this view) and the setting rings are locked. (The operating ring on the end of the rotor locking bar is visible at the end of the rotor, about 2mm out from the first pin-wheel). The comb follows the locking bar outwards, so that the long teeth on the setting rings pass between the slots in the comb.

The clearing mechanism simply over-rides the rotor lock, and allows the machine to commence a forward turn with the setting rings free to move. (An interlock at the right-hand end of the rotor prevents the handle being turned backwards).

With the rotor unlocked, the sliding comb is positioned to the right, so that its teeth align with the setting rings. As the rotor is turned forwards (anti-clockwise in this view) from the home position, the long teeth are caught under the comb. The setting rings are (in effect) pulled backwards towards zero as the rotor continues to turn under them. The handle stops after about a quarter of a turn, when all the rings are back to zero. The rotor non-return mechanism has not yet engaged, so the handle can safely be turned backwards to its home position.

On the Model 127, the over-ride control is a small metal tab next to the carriage shift buttons. On the Model 227, it is a sleeve over the rotor locking shaft, allowing the clearing operation to be performed with only one hand.

The description takes much longer than the operation - in practice it's just a matter of pushing the button, cranking forward till it stops, then back to home.