Calculator blog

Musings and comments about our common interest


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Several HP41cv and cx - Half nut!!

HP41 half nut units: CV and CX 

We have received some calculators: a couple of CV units and a CX unit - all of them half-nut. 

What is a half-nut unit? The original HP41 calculators were build with two circuits: one for the keyboard and screen and another for the processor. All parts were soldered through holes, the "old way".

Around 1985-1986 HP had developed far better circuit-making, and they developed a single circuit, surface mounted with just one IC. This model (which was done as C, CV and CX too) was called "half-nut", and the previous model was the renamed "full-nut". Performance of both is identical, but half-nuts have several more "failure modes" than the full-nuts!

We test all units with the test pack of the HP41CV Service module.

It is an opportunity to get a dependable, tested and revised HP41CV  or HP41CX with the full set of memory, 

You can add some of our modules that you can find in the HP41C corner.
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More about: HP41cv, HP41cx
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3 more HP41cl circuits here!

I have just received three more circuits for HP41cl (Monte, if you’re reading this, yes, this is how long it takes when using standard post services. Next time I’ll order UPS instead), and I have two available bodies to install them in, so one will have to wait for the time being…

If you’re reading this and don’t know what an HP41cl is, you must have been quite isolated during the last few years from calculator land. In short, it is everything you ever wanted the HP41c family to be: fast, with all modules built in, expandable (something the HP42s never was). It consists of a modern pcb circuit, completely back-compatible with the HP41cx firmware, but with much more memory than the HP41cx was ever able to manage, with all modules ever developed, many more functions, serial I/O, etc. This module is retrofittable to most “full nut” HP41c/cv/cx calculators. You can tell whether yours is a full nut by the square corners of the screen (while the half nut, more modern models, that have all logic in a single circuit, have a screen with rounded corners)

You will find more information about the HP41CL elsewhere in this website. It can easily be the last calculator you’ll ever need…

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More about: HP41, HP41cl, HP41cx
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New items in the HP41c corner

We have just included a number of additional hp41c items in the website:

  • A HP-Il interface
  • A rare, double X-memory module in a single module body
  • A touchpad module to protect the HP41c keyboard

In the next days we will include other items:

  • a Math/Stat module, boxed, with manuals and overlays
  • A Home Management module, boxed, with manuals and overlays
  • A Time Module, with manual

This way, we’ll populate the “HP41c corner” of our website. The old HP41c continues to be the most interesting calculator ever made!

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Black Friday - day one: HP41cv and HP41cx at rock-bottom prices!


As preparation for this “black Friday”, we will start giving low prices for selected items during this whole week.

There are three HP41CV in perfect state at 90€, and there is an HP41CX at 120€, as well in perfect state! Please contact me on the latter, since I have not put the pictures on the web yet (

You know all the craze about the HP41CL. This is the most powerful calculator standing right now - if you take into account the number of ROMs that are included. We find that most of the purchasers of that calculator are old users of hp41c’s. Apparently, theirs died, and/or they lusted for additional ROMs that they never managed to find. Now it is their opportunity: they get a faster calculator, with all the possible memory, and features that no one imagined at that time (the Sandmath series of ROMs, topping with the Sandmath 3x3, come to mind)

But if you’re not ready to DIY, or not willing to shell out 600 € (but having the guarantee of a good calculator, tested and working), you can start again with one of the above: the 3 hp41cv or the one hp41cx. Remember that this latter has the extended memory, extra functions and the embedded time module too!

This offer is exclusive to the EU countries!

Tomorrow we will include more offers!

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More about: HP41cv, HP41cx