## Captain Walter Fried's Fish Notes Annex to #F 71, Screed on Delta D Counts and Colossus runs## Page 2 |
Tony Sale's Codes and Ciphers |

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- 2

messages with 3, J, F as the highest letters (plain German).

- Linear combinations of the factors, of course, give linear

the constituent parts.

2. Details of Techniques.

- We normally get the first four X (Chi) - settings in pairs, - from

X4 and X5. Any run in which two X's are to be set is called a long

run : any run for only one X is called a short run.

Long runs. A long run is liable to produce a purely random score in

the neighbourhood of 3.2 sigma ; scores of 3.5 to 4 sigma are far from

being rarities. It is important to improve judgment by scoring the

best scores of runs; a chart exists, making use of the second best

competitor, giving the decibanage in favour of the best score. As a

rough rule of thumb, it has not in the past been our practice to accept

as a basis for further runs a X1 X2 result below 3.5 sigma.

- If a X1 X2 result of probability p is accepted. it can

settings as a basis. Suppose that, on the (3+4)x/1x2x run, a result is

obtained whose probability (lusing the chart) works out to be q. We can

assume that the probability of the X34 settings being right and the

X12 wrong is negligible. (This can be checked by doing the (3+4)x

count at the place in question).

- we now compare 4 theories (a) X1234 all right.

- (b) X12 right 34 wrong.

(c) X12 wrong 34 right.

(d) X1234 all wrong.