For add and subtract, the variables read from the store were converted from sign magnitude to 10's complement on passing through the ingress axis and the result converted back to sign magnitude at the egress axis, So at least at the point where addition takes place there is only one form of zero

–Tim

The basic question relates to what John Walker wrote: The value in the second Ingress Axis is subtracted from that in the first (ignoring the contents of the Primed Ingress Axis), and the difference is placed on the Egress Axis. If the result of the subtraction differs in sign from that of the first argument, or a borrow-in occurs (resulting from an overflow of the 50 digit capacity of the Mill), the run-up lever is set.

When subtracting two equal negative numbers, the result is zero, and the sign of the result – not negative – differes from the firsts argument, so the Run-Up Lever is set – or not? So can we rely for equality of counters on subtraction and the Run-Up lever, independent of the sign?

–Rainer