# 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. Nov 8, 2022 at 22:45
• Nov 9, 2022 at 1:00

## 1 Answer

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:

"The wheel-turnover notches are fixed to the index ring. Therefore, the turnover of the next wheel, will always happen at the same letter in the window, but the wiring might be rotated. (meaning the ring/rotor offset)"