## The Special Fish Report## Albert W. Small (December 1944)## Page 23 |
Tony Sale's Codes and Ciphers |

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- Wheel Breaking

which depend upon the type of traffic.)

- This is called wheel-breaking. It is an attempt, through the study

simultaneously,

thereby obtaining the X wheels as well as the Delta-D text.

- We need mathematics in wheel-breaking. Wheel-breaking procedure

further hypotheses on them. Odds in favour or the final outcome are most

important

to know. By the theory of probability, these final odds are the product of

the prior odds and all the factors derived from the individual pieces of

evidence. Because a product is involved, statements of odds and of factors

are usually made in logarithms (to base 10) called "bans;" the actual

working unit is for convenience a "deciban."

- Note the following equations in probability:

- P(E+A) = P(E) P(A/E) = P(A) P(E/A)

P(E+notA) = P(E) P(notA/E) = P(notA) P(E/notA)

right hand member of the lower, we obtain:

- Odds of A, given E = (Prior odds of A)P(E/A) / P(E/notA)

and the fraction on the right is the "factor" referred to above.

- A "pip" is the factor in favour of a hypothesis, resulting from the

- It is the custom in wheel-breaking to begin with the Delta-Z1 Delta-Z2

This rectangle is usually constructed on the Colossus, or on Garbo. The

rectangle is converged crudely by hand, by methods already familiar to

Arlington.

"Accurate convergence" is almost never used.

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