## Captain Walter Fried's Fish Notes Annex to #F 71, Screed on Delta D Counts and Colossus runs## Page 3 |
Tony Sale's Codes and Ciphers |

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Example. On the X12 run the settings 16, 09, give a score of 3.8 sigma

with a rival of 3.4 sigma. Thus the settings 16, 09 are 2 decibans up :

or p = 8/13, 10log10 p = -2.

(a) A (3+4)x/1x2x run gives X34 settings of 13, 20 with a score of

4.5 sigma and the nearest rival is 3.5 sigma : the decibanage in favour

(from the chart) is 15. Therefore 10log10(p*q/(1-q)) = 13, in fact the

whole story is 13 decibans up or 20 to 1 on.

(b) On the other hand, if the (3+4)x/1x2x run gives only a 4 sigma

reading with a 3.5 sigma rival, its decibanage is 6 up and the whole

story is then only 4 decibans up, or 5 to 2 on.

- These methods enable one to estimate the odds on the combined

- On the other hand, the X34 run may be a disappointment, and

The factor lost by the X12 settings is a function of the probability

of the correct answer, being below the observed highest answer. This

will vary with the link and the run used : experience shows that on

a Berlin end or a Paris Jelly or Salonica Cod, a reputable score occurs

about half the time - say a score of 3.5 sigma or over. So the original

hypothesis loses a factor of 2 if the (3+4)x/1x2x run has no score above

3.5 sigma. On Rome Bream or Zagreb Gurnard on the run 4=5=/1=2,

the factor is probably in the region of 5.

(i) The length of the message. The chart is based on a standard length

message and on the probability of the right score being in the various

ranges. For a very short message the right score cannot be expected to

be so high and the chart is over severe; conversly for long messages it

is lenient. A standard length might be taken to be 3600.

(ii) Slides. The highest score may well be correct on one wheel and

wrong on the other. Wheels often have good slides - (i.e. two different