# The Special Fish Report

## Albert W. Small (December 1944)

### Page 61

Tony Sale's
Codes and Ciphers

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CX/MSS
TOP SECRET Special Fish Report Page 61

Setting PSIs by "Hand"

Setting psi's involves the equation D + PSI' = P, and is therefore

a problem belonging to the Testery rather than the Newmanry. It is done

by hand just as at Arlington; but they do it much "smoother" here. Experience,

and I believe experience alone, has made these capable lads artists at their

work. The time usually required to set all 5 psi's varies: given known

patterns, and high motor dottage, they can be set in 20 minutes.

Adverse conditions can require 8 hours or more. Day in and day out,

the average time is 4 hours counting the unbroken ones in that average;

one hour is the most usual time.

The Newmanry sends the Testery a dechi, written out on width

31, plus their 32-letter count of Delta-D from Colossus. The Testery writes the X2

pattern across the top line of the dechi page,if a limitation involving PSI'1oneback

is known or suspected; or the X2oneback pattern if any other limitation is known

or suspected. The 32-letter count is then studied to determine the P-text form

of "stop"; if the 32-letter count shows U, A, and 5 high, "5M89" is indicated;

If U, O, 5, then "5M98;" but since O Is usually much higher in frequency than

A anyway, it must be quite high before "5M98" is indicated; high slants in

the Delta-D 32-letter count indicate doubling in the "stop" such as "55M889" or

"5M889."

The Testery also studies the 32-letter count to see if, in their

judgement, some X wheel could be wrongly set. (If X3 is correct, 3 should be

higher than N, U than A, J than K, X than B, G than V, O than M; if X5 is

set correctly, / than T, F than X, U than Q.) Testery finds Newman's section

fairly accurate, especially on wheel-breaking; but Testery has never forgotten

the time a Colossus operator sent them a dechi marked "all certain," which

was set on wheels of the wrong date. In fact, X3 wheel setting is quite

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