HP41C overlays


I have two HP41C overlays which I cannot determine what they are.

1) Functions on the overlay (top row) include: DCV/ACV, TEM/REF,2W(ohm symbol)/4w(ohm symbol), FRQ/TOT, RED/WRT

2) Functions on the overlay (top row) include: T/E, J/K, S/R, RTD/4WRTD, THM, 4WTHM.

2nd func is f (gold) shift - e.g. f ACV on the top left key of the first overlay.

Anybody know what these two overlays are for?




Sounds like the overlays for the HP 3421A Data Acquisition unit control module. I have the module but have never seen the overlays.


The overlays for the 3421A control module are of the protective type,

which means they cover the whole keyboard, like the 82220A protective keyboard overlay.




The 3421A was my first thought, but there are no CLS or OPN commands described, which would be used on the 3421A. So my next guess would be the overlay for an HP 3468A/B Digital Multimeter. The commands described on the overlay would be used for multimeter functions. I was not aware that the 3468 module even existed, but I can't think of any other HPIL controlled multimeter.


Is this your overlay

Here - see page 17

This would be used for a very rare module

Edited: 10 Apr 2011, 12:16 a.m.


Yes, that's one of them.
Thank you Donald.



Even though calculators are only history/nostalgia today, here it is:
overlays looked like smart thing initially, but turned out to be useless.
Experienced user doesn't look at key legend anyway.


...but turned out to be useless. Experienced user doesn't look at key legend anyway.

Oh - so you asked every experienced user and the results were unanimous? I wholeheartedly disagree, so here's a 32-year HP41 user feeling the opposite way. Making "declarations" like that seem foolhardy to me. Plus, the blank overlays were great for markings for new programs with a new set of assignments. They may not have sold well from HP, but that may have been due to the relatively high cost.

Jake Schwartz


What I wrote is my observation only. All people I know using HP41 *knew* their module user keys so did I.
I believe you asked every user out there with the exception of the ones I know and they can't live without overlays; I didn't so I'm sorry for not been clear enough.


Overlays on the 41 were just great, and continue to be. Its user interface has the power of a juggernaught and the simplicity and elegance of a keypad, talk about ease of use - can you spell Soft-Alpha? No thanks.

That of course assumes that you use the calculator for multiple, different aaplications. The USER keyboard(s) will be impossible to navigate without the overlays as visual keys.


Well that assumption solves the problem. As a surveyor I never used the overlay. I used to work with structural engineers and they knew their user keys and I have never seen them using the overlay.
I agree if someone uses multiple modules overlays would be necessary, but I do not know such people.


yeah, I think it's called "splintered personality" :-)

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