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Figure 2: ECM Mark II - Cipher/Control Rotor & Index Rotor [9]

When the cipher and control rotors are inserted in the normal orientation, the current 

position is shown to the user as a right side up letter that steps in reverse alphabetic order 

(assuming the rotor is in a position that will step). For example, in Figure 3, a rotor inserted 

in the normal position at letter O will have the letter P above it and the letter N below it. If 

the rotor steps, the current position will change to N with the letter O above it and the letter 

8

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M below it. If the rotor is inserted in the reversed orientation, the current position is shown 

upside down. Using the same example for the normal orientation, except with the rotor 

inserted in the reverse orientation (Figure 4), the user would see an upside down O as the 

current position, with an upside down N above it and an upside down P below it. If the 

rotor steps, the current position will be an upside down P with an upside down O above it 

and an upside down Q below it.