About this simulation
The Lorenz SZ42 here has its real wheel sizes and stepping rules, without the "limitations" (extra key-stream rules of the SZ42A/B that were in use on many links during 1944), and the ciphertext is enciphered the real way: plaintext plus the χ stream plus the extended ψ stream. The messages are invented German in the style of the traffic, typed with the operators' habits (9 for space, doubled shifts), which is what gives the statistics their bias.
Colossus's 1+2 break-in counts exactly the test Tutte devised. The short runs that set χ3, χ4 and χ5 use a simplified choice of impulse pairs; the Newmanry chose from a larger set of runs. Wheel patterns are assumed known, as they historically came from separate wheel-breaking. The Testery found the ψ and motor settings by hand; this page narrates that step and applies the true settings.
The machine's look is an illustrative composite of the wartime photographs and the rebuild at The National Museum of Computing, not a measured drawing, and the counter lamp displays are a stand-in. The sounds are synthesized.