Thank you Jarlve. Here are the results:

Bigrams:

Trigrams:

Quadgrams:

The spikes at P2 are interesting.

But one thing I don’t understand: Let’s assume that z340 was created in the "crossed lines" way. In this case, the horizontal and vertical trigrams and pivots would be the corresponding features of the cipher. What’s the point of destroying these supposed features and measuring the result?

Thanks Largo.

The spikes at P2 are interesting.

Indeed. Your crossed lines transposition idea is simple, effective and original and the pivots may just hint at this. I do foresee a problem with the search space if the scheme is fully unleashed. So in that way it may not be simple. If every new line could be either horizontal or vertical at any position then the search space becomes problematic. If this transposition was done during or after homophonic substitution then it should show up on my test and most of the lines should be horizontal considering the sequential properties the 340 has. But perhaps we are not looking at the 340 in the right dimensions or the crossed lines in the 340 are a bit different and not as straight forward.

But one thing I don’t understand: Let’s assume that z340 was created in the "crossed lines" way. In this case, the horizontal and vertical trigrams and pivots would be the corresponding features of the cipher. What’s the point of destroying these supposed features and measuring the result?

I was trying to answer your previous question:

Do you also have any idea for the P1 spike in the bigrams and the P1 spike in the trigrams?