Enigma: Actions involved in the 'Double Stepping' of the Middle Rotor

In this description of the Enigma rotor movement sequence the following conventions have been adopted. The three rotors are numbered from right to left as seen from the machine operator’s viewpoint thus, the ‘fast’ or right hand rotor is Rotor 1, Rotor 2 is in the middle position and the ‘slow’ or left hand rotor is Rotor 3. The associated ratchets, stepping levers and notches are similarly designated. e.g. Ratchet 3 is attached to Rotor 3, the primary function of Lever 1 is to move Rotor 1; Notch 2 is on the index ring of Rotor 2; ...and so on. Following this same convention, “left” and “right” in the body of the article are as seen from the viewpoint of the Enigma keyboard operator.