25C/29C Conditionals

[Thomas Okken]

Educated guess:

The early programmable models with eight comparison functions, that is, the 25/25C, 19C/29C, 67/97, 33E/33C, 11C, and 16C, all have the same set: X=0, X≠0, X<0, X>0, X=Y, X≠Y, X≤Y, and X>Y, except for the 25/25C, which has X=0, X≠0, X<0, X≥0, X=Y, X≠Y, X<Y, and X≥Y.

So the 25/25C are different, and I suspect it is significant that the comparison functions on those calculators are more symmetrical: the comparisons with 0 exactly match those with Y, and all comparisons consist of pairs that are exactly complementary. This would have made it possible to implement the 25/25C comparison functions using less code, and given that the HP-25 ROM is completely full, that may have been the only way they could make everything fit.