The Special Fish Report
Albert W. Small (December 1944)
Codes and Ciphers
TOP SECRET Special Fish Report Page 58
The problems of wheel-setting and wheel-breaking have been
presented without regard to motor limitations, because in general
such limitations are ignored. It is a fact however (see Fried #96)
that most of today's circuits use limitations of some form or other.
If the limitation is simply X2 it can be used to advantage in the
"stickier" Colossus runs: for instances in wheel-setting, operators may
"look at" only those positions wherein X2oneback = x, and thereby gain approximately
20% in expected causal sigmage (more or less depending upon motor
dots) the bulge occurs mostly on X2oneback = x positions. This fast
is also of value in "wheel-breaking" the Delta-X2 patterns. High pippages
in the Delta-X2 wheel can be expected at points wherein X2oneback = x and low
pippages at X2oneback = . positions. Thus a preliminary pattern can often
be completed by inspection of the worksheet, utilising this knowledge as
a guide to marking in the X2oneback = x positions, and working this back and
forth with Delta-X2 values already in.
Motor and Psi Runs
Last spring when Chi and Psi pattern remained permanent throughout
each calendar month, the setting of Psi's might possibly have become a bottleneck.
At that time the Newmanry used to make Motor and PSI runs to help the Testery.
But this is done only about twice a week today, because the pressure to
get out Chi's daily is too great.
However P5twoback limitations is beginning to disappear from the networks.
The desirability of resuming motor and psi runs on a larger scale has therefore
The principle of motor runs is simple. Bulges in the Delta-D result