The successful working of all parts of Mr.Newman's section depended on the
accuracy and efficiency of the Tunny rooms which were responsible for looking
after all copying, reading and tape-making machinery.
An elaborate system of cheeks for all tapes made was found to be essential
to prevent the early introduction of mistakes which might be reproduced unnoticed.
The importance of checks was not realised at first and it is generally believed
that the comparative lack of success in the earliest days was largely due to the
use ofincorrect tapes.
35B GENERAL RULES
All tapes were made twice independently and compared to ensure that no
letters had been inserted or omitted. Before newly-made tapes were returned to the
appropriate registrar their text length was measured on a Hand Counter and marked
on the tape. All jobs involving the making of tapes (or prints) other than exact
copies, were sent to Tunny with a Hand Check for the beginning which had been
worked out by the Registrar. For every tape made two copies (at least) were
ordered to save time in case of damage to one of them. All work was very fully
35C CHECKING AND ALTERATION OF TAPES
(a) Checking tapes against Red Forms
This was not strictly a Tunny Room job, but may logically be described here.
For a long time every long rectangling tape and every setting tape which failed to
set was checked against the appropriate Red Form.
First Method The number of letters on each page of the RF was calculated and the
first few letters at the top of each page recorded, The tape was wound through the
hand counter and stopped at the calculated position corresponding to the end of
each page. The position of the entries corresponding to the top of the next
page were checked on the tape.
Second Method The tape was measured out on a hand counter, marked at every
multiple of 1271, and 10 letters after each mark recorded. When the RF arrived,
the letters at similar positions on it, were independently noted, and the results
compared. This method was suitable for rectangling tapes as it enabled a hand
check for the rectangle to be made at once from the tape check.
(b) Comparing two versions of the same tape
It was sometimes necessary to compare two versions of the same tape, ( say
an original version with its rewrite). The tapes were added together on Miles
until the output tape showed that there was a slide. The place at which this
occurred was marked on both tapes and the tapes were reset (to account for the
slide) and the operation continued. A print-out of both versions was made on Garbo
wherever discrepancies had been noted so that Knockholt could be asked to reread
the undulator tape at these places and decide which version was the most likely. A
composite tape could then be made embodying the best of both tapes.
(e) Correction and Doctoring of tapes.
This was normally done on an IBM (preferably) or Angel. The tape to be
corrected was marked (with the help of a hand counter) at the places at which a
letter was to be inserted or omitted. The IBM or Angel was stopped when the marks
were reached and the correction made.