# The Newmanry History

## Part of the General Report on Tunny (1945)

### Page 289

Tony Sale's
Codes and Ciphers

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36C Page 289

(c) Checking of tapes.

Needless to say the long tapes ordered on A (or B) procedure for rectangling
needed to be particularly carefully checked. Therefore they were checked by us
against The Red Form, as described in Ch. 35. However, after Knockholt had been
supplied with a hand counter in Autumn 1944, There were so few mistakes that we
stopped checking the tapes in Bletchley.

36B RECTANGLES AND CHI2 CAP RUNS

There were four methods of rectangling, decried in ch. 24. Priorities were
decided by intelligence value, length of tape, supporting tapes and many other
considerations. Tapes were often rectangled in parts, in case of a slide in the
tape. The Sum theta(i,j)^2 test was done when the Colossus had the required
meter.

In addition chi 2 cap runs were done on each third and the whole of each
message rectangled.

If X >7(tau)^1/2 the WM might start Colossus chi-breaking at once, before
the rectangle was converged. If 5.6(v)^1/2 priority. Very rarely the chi 2 cap run revealed a slide in the tape.
(See R5 p.98.)

36C TIMES

Here are the average times in hours for various processes and over various
periods. The unbracketed figures are for high priority and bracketed for low
priority groups.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
W.S. 33.
Serial No. Date TS. TE. Lgth.

R/F. Checked

Remake

Ops.

Rectangle

Converged

Significant

Returned to Ops

Action
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Rectangle card used by H Registry.

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