If the Q panel were used delta Z2 would be switched in along with delta Z1.
This could be avoided, alternatively, by splitting the delta Z selecting switch.
(iii) the run i=2=lim (i.e. Delta-D1 = Delta-D2 = X2oneback can be switched and
1=2 on the Q panel, multiple testing on X1
Q2 + X + TM = . on the plug panel
TM = not X2oneback on the limitation determiner switches, using BMc/o,
53L MULTIPLE TEST
(a) To save time it is arranged that the same wheel can be examined at five
different settings simultaneously, the five scores appearing in the five counters.
(b) Memory circuits
When the multiple test switch for any wheel is thrown, a memory device is
switched in, which stores the characters of that wheel 1,2,3, and 4 places back.
Footnote More explicitly Colossus remembers characters of the wheel opposite
places on the tape 1,2,3,4, back; in particular characters of PSI' not of PSI .
In the first four places of the text some of the remembered characters are really
those at the end of the text in the preceding tape revolution; and will give
random scores, unless the text length is a multiple of the wheel length: it is
customary to span from o4 onwards.
Thus when Colossus is examining a particular place on Z, it has available
(i) on the multiply tested wheel, the present character and the characters
1,2,3,4, back. These are associated with the numbers 1,2,3,4,5 ( i back with
(ii) on Z, and on all other wheels, only the present character.
Most operators are surprised to find that the remembered characters appear
nowhere except as a component of Q, the corresponding five characters of Q are
e.g. if X is multiply tested and Q = Delta-X + Delta-Z then