HP-41C how to determine if it's halfnut ?


I have an HP-41C built in 1980 that has the halfnut display. Is it possible that such an early HP-41C has the halfnut electronics inside ? Is it possible to tell if the electronics inside is the halfnut or fullnut without opening the calculator ?


My approach is not 100% sure: Use a synthetic tone that leaves the beeper in "buz mode". Halfnuts tend to "buz" louder. But you know the old surgeon saying: "Open it if you want to see clear."



1) No HP41 of any sort actually made as early as 1980 was built as a halfnut. That didn't happen for several years afterward. The orignal HP41s from 1980 would all have been fullnuts. There's just no way around this. HP did not change the HP41 manufacturing process that early. Period. :-)

2) If you actually HAVE an HP41C with a 1980 S/N on the back and a halfnut front / display, then it must be the result of either a) some sort of repair by HP where they replaced the front half of the calculator and left the back side of the calculator alone, or b) some sort of swap by a user/owner trying to get a calculator working again.

3) One way to test would be to take the back of the calculator off and take digital pictures to post and let some of us look at it. That would help determine the true inside nature of the beast.

4) Another way to test would be to load up the Sandbox ROM onto a Clonix / No-VRAM module (what? you don't have one of those?) and try out the lowercase display characters.

My feeling is that it is probably a result of one of the things listed in #2 above.


It's my father's calculator and he never modified it by himself. You're right, it was probably repaired once and they changed the display and the electronic inside. It may be a coincidence, but I have another HP-41C with serial 2013A which is also a halfnut.

Anyway, Raymond del Tondo (many thanks to him) gave me a good advice in order to check if it was a halfnut : He told me that halfnuts were lighter than fullnuts and that 41C and 41CV should weight about the same. By chance I have a fullnut 41CV and its weight is 147g compared to the 125g of the halfnut 41C. So my 41C is definitely a halfnut !

Thanks all for your advice, I will update the description on my auction on ebay (yes, shame on me, I'm selling my father's calculator :o)


I don´t think it is that easy. You have to compare two HP-41C, not a CV with a C. A CV has QuadMEM, so there is more electronical stuff in it. So, the weight must be heavier.
What do you think?





Hi Matthias,

the extra mem chips of a CV don't have much weight.

I think even a CY is lighter than a fullnut C;-)



Raymond, do you have a CY? That would be new to me? Where did you get this from? I always thought, I was in advance...


Hello Matthias,

Why not check it for real ? It would be interesting to see the results !

I have weighted my calculators without any port cover, side cover and battery of any kind and I have :

125g for the HP-41C halfnut

146g for the HP-41CV fullnut

132g for the HP-41CX halfnut

Do you have the weight of the one I'm missing (41C & CX fullnut and CV halfnut) ?


Whats all the fuss? Just look at the display.

If it has rounded corners, it has to be a halfnut internally since the LCD versions are completely different.

The weight of a halfnut C and halfnut CV are the same.

The fullnut C's and CV's will vary in weight due to internal version differences, 25g or more would not be uncommon.

Edited: 24 Feb 2005, 5:46 p.m.


I didn't know that the LCD display was linked to the new eletronics inside. I thought it could be possible to have a coconut eletronics with a halfnut display.


According to Richard Nelson's and Jeremy Smith's article entitled "HALFNUT-- AN INTERNALLY IMPROVED HP-41C,CV,CX" in the CHHU Chronicle V2N4 Jul/Aug '85, pages 9-11, HP started the Halfnut project in mid-83. At the time the article was written, it was expected that cv and cx halfnuts would start shipping to dealers in Sep '85, and that the 41c Halfnut would only be used for service of returned 41c's. So If you have a real 41c Halfnut, it would have to be from having been serviced after the older stock (Coconuts) had already been used up. BTW, if a 41 is not a Halfnut, it's a Coconut, not a Fullnut, according to HP's internal project names.

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