(i) Reversing one or more of the five impulses.
(ii) Making blank one or more of the five impulses.
(iii) Running backwards.
(iv) Encoding with P5 limitation.
(v) Innumerable switches for cutting out lamps.
Tunnies "1" and "3" can produce differenced tapes.
56L. DECODING MACHINE. Fig 58(xxiv).
(a) General description of operation.
Given a cipher text all of whose settings are known, the appropriate
patterns, settings and limitation are imposed, and the machine is started.
As each letter of cipher is typed out on the keyboard, Chi, Psi, are
automatically added so that a letter of clear text is printed.
In place of the keyboard an auto-transmitter reading a cipher tape can be
plugged in, but its speed is apt to be too great for the machine.
The settings of all wheels at each letter are shown by indicating lamps.
For swift operation some switches are on a control box adjacent to the
(b) Wheel patterns.
See 56K(b), but there is no display of positions moved through, only of
(d) Chaser settings.
In early models if it were necessary for any reason, such as typists' error
or corruption, to start again a few places back, the position of each wheel had to
be calculated and set separately. This is now avoided by "chaser settings" which
are stationary during ordinary running, but
(i) the "set reading" switch causes the chaser settings to move forward to
current settings (used once per line or so)
(ii) the "reset" switch causes the current settings to move back to the
These switches are duplicated on the control box.
The same lamps are used to indicate both current and chaser settings, but
confusion is avoided by "DCL" which extinguishes the chaser settings.