An HP-35 Production Overview

[teenix]

After flipping through the "Remembering the HP-35" document, which is very interesting, on page 6 it mentions the bug was caused by a "6 bit programming error".

I don't know how the 6 bits figure into the changes in the .0002 ARC TAN error, but in the later HP-35's, the way one of the division routines was entered was changed after doing an arc tan math routine. This changed the A and P register values.

At the end of the division in the early HP-35, the result in the C register was 1, whereas in the later HP-35's the result in the C register was 2.

If at this point the C register is changed to 2, then after all the remaining calculations in the early HP-35 were completed, the result came out ok.

I haven't checked the other errors, as they may have other compensation mods in the code.

cheers

Tony