Calculator blog

Musings and comments about our common interest


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Good news: HP41CL is coming back !!!


I was informed by Monte Dalrymple that he has sent HP41CL modules to production again. Apparently these can be here by August - so back again the most powerful tru RPN calculator !!!

Apparently, no changes in performance. I will order only units equipped with Time Module. Please connect to if you are interested in getting one !



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HP1CL is over!

tall_keys_-_5We have sold the last unit of HP41CL. So far there are no more made and no more planned - and it will be difficult to produce more since there are many parts that are out-of -life. The board would require a deep redesign which current demand does not warrant - so it is a pity for all of us!!

One of the last units sold was a 1937A serial number unit - one of the very first. I have only seen an earlier unit, a 1932A. It is a nice closing to the story, 43 years after its inception in 1979. I was there then and I remember the lust for that powerful machine, far from me as primary student. My father bought instead a HP33c for me - which hooked me into RPN - a hook that I have not been able to unleash so far.

With the so-far demise of the HP35s, there are now the HP12C, the HP12C platinum (which has an RPN mode), the HP17bII+ and the Prime as RPN machines. So far in Europe the HP12C has been absent for some time, but I have been promised that it is returned - so far that I have been able to place an order for them. I expect the order to arrive before month end.

We are missing a RPN scientific (not graphical), preferably of small size, not competing with bigger student units. I have been given hope by the current calculator management - let's see!


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More about: HP41cl, hp15c
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Ideas for a HP41c module

tall_keys_-_5Some of our readers know that the other of my passions is audio. And more and more the DIY variety - so there are many calculations there. 

I would be very thankful if you could provide me with formulae or programs for audio design, or direct me to sites that have them. Some of the items I'd like to cover and integrate in the audio module:

  • Thiele/small parameter calculation for loudspeakers
  • Sound pressure -loudspeaker efficiency - amplifier power relations
  • Filter component calculation
  • Room resonance frequencies
  • Amplifier feedback component calculation
  • Triode model for a local operating point.

You get the point. Please contact us at with equations that you may want to have included in the module! This should come accompanied with some manual too.



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An early HP41C converted to CL

I have prepared an early HP41C (serial number 1944A...). I write it here because initially I put it on sale with not good enough pictures, but now it comes in all its beauty.

It is so early a model that it has tall keys and the original, early metal plate keyboard surface (not textured plastic)
















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HP41CL with Time Module

For some time we have left aside the blog, due to lots of repairs and CL installations. Then comms are postponed and the urgent orders come forward

So we have not informed here that there is now the possibility of integrating a Time Module in the HP41CL. This saves the user a 120-140 € module, and a slot. 

All the rest of characteristics and features of the CL are still there, while the list of included modules is continuing to grow. Also many of the modules designed by Angel Martin have been reviewed, debugged and improved.



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More about: HP41cl
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The beauty of RPN

A short one (very far from the long posts involving repairing manuals):

One of my sons is learning to do divisions, and he has to practice. So I took the HP41CL to generate random divisions. I always have among the modules virtually plugged in the system Sandmath 4x4, which has the function RND (I think it is there - the only thing for sure is that having only the advantage pack and Sandmath, it DOES work), so I made this short program in all of 1 minute, plus other 15 seconds to assign it to a key:



3 1E2

4 *


6 1E6

7 *


It stores a 5 digit number in X and a 2 digit in Y. My son can execute it and press x<>y in order to get the divisor too.

There is no way I could get a faster solution with a computer or any other more modern calculator!!


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More about: HP41cl
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A brief description of the HP41CL

We have now 3 more circuits to be built on HP41CV bodies. These were just uploaded with the very latest versions of all modules.

The news is that we have a Time Module available to create the ultimate classic calculator.

The first order will be shipped with an original HP41C oversized vinyl case. Next units will go with leather-like new cases.


For those that are not aware of the capabilities of this machine, here are some of its features:

  • All features of an HP-41CX except for the Time Module. CX Time functions (the soft- ware) are included, but a Time module plugged into a Port is required for full timer functionality. 
  • Full 600-register Extended Memory is built in.
  • Over 295 plug-in module images are built in. Functions are included to allow these images to be virtually plugged into a calculator Port and unplugged from a calculator Port.
  • Turbo mode, which allows the calculator to run at up to 50X normal speed. Actual values available are 2X, 5X, 10X, 20X and 50X.
  • Several empty pages (4K in length) of Flash memory are available for non-volatile storage.
  • 122 pages (4K in length) of RAM are available. All RAM is continuously powered.
  • A sophisticated Memory Management Unit (MMU) allows full access to the large physical memory.
  • Full bus compatibility for the Ports, allowing the use of any peripheral designed for the HP-41 system.
  • A full-duplex serial port is available when the optional serial connector is used. This optional connector uses a 2.5mm stereo jack mounted in a blank port cover.

Please see all options in the HP41CL page. Prices start at 625 EUR.

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More about: HP41cl
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Offers for Black Friday - 1

Now that Christmas is close, it is the time to think about gifts for others - and for yourself. You can recall your youth, and the time when you were longing for an HP41c, and you had to settle with a lower choice; or you could afford it, but not the wealth of modules and options; or you had it, and got it lost, stolen or damaged beyond repair. Now you have the opportunity of having it back!
With a new processor, totally compatible with the original Coconut CPU but 50 times faster, having burned in its memory the contents of all known program modules and then some invented by today's programmers, and carefully assembled on pristine bodies without corrosion or screen damage, you can now buy the HP41CL from
  • 50 x speed compared with the original; Switchable to several speeds including the 1:1 original.
  • All known software modules of that time
  • Many new modules designed lately, including the Sandmath family, an HP16c emulator, complex numbers, advanced matrix, etc.
  • All the addressable memory of the original
  • Additional flash memory where you can download and write new modules.
  • Possibility of a serial module to download new modules and capabilities from your PC
  • Compatibility with all external modules and interfaces (time module, infrared module, printers, barcode readers, interfaces, etc.
Pricing: usually 625€; 550€ during the Black Friday period, and 625€ if we include a time module with manual. For more options, please look in our website

Limited to 4 units only.
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Comments on HP41CL troubleshooting

The users of the hp41c machines need to be careful while taking their calculators on a trip. The machine is sensitive to vibrations, and doesn’t have as big a capacitor as the original one (which could allow you to change batteries taking your sweet time, and all the programs and configuration would still remain). It has happened already a couple of times that a calculator sent has lost its configuration, or even wouldn’t start.

We reviewed the case in this blog issue, but we think it is relevant - when you buy such a expensive calculator, you need to be sure to be able to revive it when it has a hiccup!

The question comes then on how to initialize the calculator. There are different possible initializations, but in have to confess that this is beyond my knowledge. The only thing that I want to make sure of, is that library #4 is installed in page #4. This library comprises several subroutines that are used by a number of modules programmed and/or compiled by Angel Martin. Basically these are the sole modules being developed today, and include an interesting clone of the hp16c, the extremely powerful Sandmath modules (which turn the hp41 into a very powerful mathematical machine), the advanced matrix ROM, the Complex Functions ROM, the matrix/polynomial ROM and other operating systems and toolbox-oriented ROMs. The interesting thing is that it doesn’t use any of the typical ports, so you are free to use all your modules (also taking into account that, if you plug in the real Time module, it doesn’t occupy the corresponding pages since its functions are already in memory in the hp 41cl)

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New HP41CLs available


Due to the complexity of getting the right shipment option for the hp41c battery repair kit (it depends on the stage you are in the order), we have decided to increase the price a little and include the shipping cost in it. This is particularly beneficial for those out of the European Union, since they save also VAT.

Now the ordering should be much easier. Orders have begun to come in, so it must be working better than before!

On another subject: during this week end, we assembled 2 new JP 41CL with the latest circuit, including the new modules from Systemyde and Angel Martin (namely the HP16c function set clone). So, there are now 1 tall keys, satin-keyboard HP41c and 2 low keys, rugged keyboard HP41c. On demand, we could assemble too an HP41c - but personally I have always preferred the white border of the c models than the yellow of the CV or CX. Screen and keyboard are top-notch in all cases. No original box available, sorry!

There are also two Time modules available, one with English manual, and the other with French manual and original box. These are sold at 120 € if demanded with any of the HP41CLs, 150 € otherwise.

(As a comment aside, some customers complain that they can find some items cheaper in internet - but please compare apples with apples: our products bear 21% VAT on the sales price, provided that the customer sits in the European Union - hence a significant difference! Most second-hand dealers in the action sites don't charge VAT (and don't pay charge VAT to their tax administration!)

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