HP-35 Version 1 Red Dot


I recently acquired an HP-35 Version 1 Red Dot, and discovered an interesting ROM firmware design variant as compared to later versions of the HP-35. Whereas you can enter the negative sign of an exponent either before or after entering the exponent digits and the negative sign can be toggled on and off at any time, neither is possible with the Version 1 red dot. The negative sign MUST be entered first, and cannot be toggled off once it is entered. I also own a Version 3 and Version 4, which can be toggled, however, I do not own a Version 2, so I don't know if this peculiarity applies only to the Version 1 Red Dot. The Red Dot is S/N 1143A04281.


This page explains some of the ROM versions. My version 2 pre-bug-fixed 35 has the EEX/CHS bug that you describe, so I think that the EEX/CHS bug was only released when the fix was done for the exp(ln(2.02)) bug and trig bugs. The "errata" card that HP sent around to owners at the time does not mention the EEX/CHS bug.

Edited: 5 Jan 2009, 2:25 p.m.


Thank you for your reply. I suppose HP may not have mentioned this oddity as a "bug", since it does not result in erroneous results; only affects ease of operation. I find it curious that the manual supplied with my Version 3 specifically states on page 13 that "To enter negative powers of ten, you MUST press CH S (Change Sign) BEFORE keying in the power of ten." However, the Version 3 does not have this problem, so perhaps this manual was prepared by HP prior to the fix being implemented. Do you have a manual for your Version 2, and if so, what does it say in this matter? My Red Dot manual simply gives an example in which the exponent negative sign is entered prior to the digit, but does not elaborate.


I agree, it's not a bug.

My manual (no revision number) which I received with my version 2 pre-bug-fixed ROM states on page 13 "you must press CHS before keying in the power to ten".

The color manual (REV 8/73) on the Museum CD/DVD states on page 13 "press CHS after pressing EEX and either before or after keying in the power of 10"

So HP was totally on top of this issue and 100% correct in their manual. I sure wish the same was true with the current HP calculators and manuals.

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