and the start of every 20th line on the print verified.
Lines of the de-chi were numbered and the print marked with the 1st 10
letters of Z.
If the Delta-D count on the de-chi tape did not check the wheels set up on
the Tunny machine were checked and if no mistake was discovered the Z tape was
recounted on a different Colossus.
(b) With Colossus check
The Tunny room was supplied with a chit giving setting and wheels and a
Colossus check giving the following letters of de-chi :- 2-9,62i-624,1241-
1244,1861-1864,2481-2484, 3101-3104 and the last 5 letters. To this the Tapes
Registrar had added the settings for letters 621,1241 etc.
The de-chi was made on Tunny twice. The first make was stopped
automatically every 620 letters and the settings checked. This make was printed
while the second make was being made. If the two makes were identical, and the
print checked with the Colossus check the de-chi was assumed correct and marked
and sent over as before.
When the two makes agreed, but the print did not agree with the Colossus
check, the Tunny wheels were checked and if correct, the Colossus check was
assumed invalid, a hand check made, and the de-chi tape stuck and counted on
(c) Contraction of de-chis
In days when psis were set on Robinson (on messages with X2oneback lim) the
psis were run against a de-chi tape from which all letters occurring against Total
Motor dots were omitted. The contracted de-chi was made on a Tunny on which motors
and X2 were set up. A special switch was used and a hand check supplied.
35F WHEEL TAPES AID TEST TAPES
(a) Chi test tapes
These were made on Tunny. The appropriate wheels were set up at 01 01 01 01
01 and 2002 letters of chi-stream perforated. Before sticking for Colossus every
impulse was checked by sliding the tape against itself at a multiple of each wheel
(b) Psi test tapes
These were made on Tunny with setting 01 01 01 01 01 for Psis and 01 01 for
Motors. The limitation appropriate to the wheel-day concerned was used and a hand
check of 61 letters supplied by the registrar. Final copies were stuck for
(c) Motor tapes
Tunny can be made to perforate Basic Motor tapes from the plugged patterns
of M37 and M61 and Total Motor tapes (for X2oneback lim) if X2 also set up.
Motor tapes were sometimes required for printing the motor over a dechi or for
doing motor runs on Robinson. A hand check of 15 letters was supplied.