# How do the notch and window positions on an Enigma machine correlate?

I am having difficulty visualizing the stepping process.

The permutation of Wheel I of Enigma I is as follows:

ABCDEFGHIJKLMNOPQRSTUVWXYZ
EKMFLGDQVZNTOWYHXUSPAIBRCJ


For this rotor, the stepping notch is at Y. The literature states that the letter Q is visible when the notch is positioned, and after the step, R is visible.

It is my current understanding that the lower (exit) row increments with every character entry (which would be represented here by a circular shift), and when it gets to the notch, a step of the next wheel occurs. My question is, what is the configuration of the lower row with respect to the upper rows at the notch step? If Y is the final character in the lower (exit) row (26), then Q is in position 19 in the upper row. Shouldn't it be at position 1? Or conversely, when Q is in position 1, Y is in position 8.

Are the notch sensor and window always 7 contacts apart (on this rotor), or are they both relative to some other component?

Can someone provide a diagram of where this rotor is prior to the step (i.e., notch Y and window Q)?

• Just a few editing hint: using double spaces (for a soft return) doesn't always visually separate the parts. Easier to just start a new section (double enter). Similarly, in normal text the sans serif fonts are great, but for single letters you can use the back ticks to indicate code (which uses a monospaced serif font). Or, on a few sites as ours you can use $\LaTeX$ of course. Commented Nov 8, 2022 at 22:45
• Commented Nov 9, 2022 at 1:00

Looking more closely at the various wiring configurations, it turns out that for a given machine, there is a constant distance between notch and window on the ring having nothing to do with the rotor. For instance, Enigma I has Q-Y, E-M, V-D, J-R, Z-H for rotors I-V respectively, all of which are 8 characters apart mod 26. Same goes for each of the 2 notches on rotors VI-VIII of Enigma M3 (Z-H, M-U). The fixed distance is actually mentioned in a nonexplicit fashion here: