The Special Fish Report

Albert W. Small (December 1944)

Page 97

Tony Sale's
Codes and Ciphers

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CX/MSS
TOP SECRET Special Fish Report Page 97

to make each run in two parts, looking at even offsets of one tape

with reference to the other on the first run (by plugging Robinson to

count only where Level 5 of tape 1 (control level) plus level five of

tape 2 (control level) = dot), and looking at odd offsets of one tape

with reference to the other on the second run (by plugging Robinson

to count only where level 5 of tape 1 plus level 5 of tape 2 = cross.)

This does not take twice as long, because the tapes are in effect

slid 2 positions at a time with reference to each other in each run,

and the over all time is the same as if only me one run were made and the

tapes slid one position at a time.

The two tapes are placed on Robinson and the Robinson

set to record all positions wherein simultaneously:

P tape level 1 + DELTA of (Z tape level 1) = dot.

P tape level 2 + DELTA of (Z tape level 2) = dot.

P tape level 3 + DELTA of (Z tape level 3) = dot.

P tape level 4 + DELTA of (Z tape level 4) = dot.

P tape level 5 + Z tape level 5 = dot for even runs
or cross for odd runs.

In other words, Robinson is plugged up to record positions wherein:

Delta/93 (DeltaP2+P5twoback+DeltaZ2) = Delta/124 (DeltaP2+P5twoback+DeltaZ2) =

Delta/279 (DeltaP2+P5twoback+DeltaZ2) = Delta/341 (DeltaP2+P5twoback+DeltaZ2) = dot

and the causal probability for such is b^5 + (1-b)^5 whereas the random

probability is 1/16. Such a run is much stronger than a run on a single

impulse of the special tapes, wherein causal probability is b^2 + (1-b)^2

as against a random of 1/2.

A sample Robinson crib run as described above is shown next page,

and described in the pages to follow.

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