# Captain Walter Fried's Fish Notes Annex to #F 71, Screed on Delta D Counts and Colossus runs

### Page 1

Tony Sale's
Codes and Ciphers

| previous page | next page | index page |

ANNEX to #F 71
Elementary Screed on Delta D Counts and Colossus Runs

1. Delta D Counts.

There can be no universal criteria for determining the
correctness of a de-Chi along the lines of insisting on a certain specified
letters having a high frequency in Delta D.

Delta D = Delta P + Delta Psi' Whereas Delta Psi' has a count
that is reasonably settled (given "a"), Delta P will vary strongly from message
to message.

The factors determining the shape of the Delta D count are, of
course, many: there are a few that we normally take into consideration
and that we believe to dominate the count.

(i) Doodling Habits. Some operators nearly always double a 5, others a
5 and an 8; some double the 9 between words. These vices, of course,
bump up / in Delta P, Some tend to put 89 between words, or to indulge in
strings of 898989 : this sends up the count of 5 in Delta P.

(ii) The proportion of punctuation. (A lot of punctuation is likely
to be due to many abbreviations). A high frequency of full stops sends
up the counts of U and 5 and (to a lesser extent) of A or O or both.

(iii) The order of 8 and 9. Most operators use 89 to return to letter-
shift : some use 98. Since the commonest letter before 89 (or 98) is
M this influences the frequencies of A and O.

(iv) The proportion of plain German. The Delta P counts of plain German
differ notably from those arising from punctuation, figures and
abbreviations etc. The typical Delta P count of message strong in plain
German is rich in J, F, 3, fairly rich in S and U.

A given Delta P count will be largely interpretable in terms
of these factors. The characteristics carry over also into the Delta D
count with the bulges, of course, much feebler and with smaller
antipodal bulges on the opposites and near-opposite, (e.g. if the
Delta P is strong in 5' s, the Delta D wll in consequence be strengthened in
9's and to a lesser extent in /, S, I, N and H). One should therefore
? line missing ?

| previous page | next page | index page |