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Calculator blog

Musings and comments about our common interest


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3D side cover


It has been a long time since the last time I wrote in this blog. Since then, we have been occupied designing new pieces - some of which are still in the development phase. We will come back to these when we have tested them. But today we would like to introduce you to the Side Cover.

Side cover

The 3D piece uses a different production method, using the new HP 3D printers that will revolutionize the industry. The surface quality is much better than the common nylon, and although it is blacker than the original model, it looks the part and can be used without problems in the calculators. Also, dimensionally is much better than the other examples we have seen in Shapeways! It took some effort and a lot of measuring to get a cover that fits so well on my HP.

Price-wise, the way we produce it allows us to maintain a very competitive price: 6 EUR each + shipment.

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Continuation on new repair aid piece

I have now an old HP41c where the upper circuit is pressed down to the zebra connectors via nuts. Now, it is difficult to ensure an even pressure and I am having problems with some of the digits. But if we force the nuts, I may break the post - as it has happened in other cases. These are the situations our new piece (wait until we can put it on sale) is made for.

This piece is intended to be put on the lower posts (where it fits tight to aid in case of cracked posts) and gives the necessary mm. of thickness so that the back side of the original type can pass the pressure on the circuit so that it stands firm on the zebra connectors. This negates the use of nuts, which can be changed only a couple of times, lest they break the thread of the post (or the post directly, as it has happened to me a couple of times). I am testing different thicknesses to find which will be the final product.

Say goodbye to the nuts!

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A new product for HP41c repair

We have now prepared a couple of new products designed to solve more HP41CL repair problems. We will discuss today the first one.

Our bent to do c to CL conversions has led us to specialize on full nut repair, instead of half nuts. But some of the tools and methods are also valuable for half nuts too!

The first of the new items we have created is the adaptor to replace screwed nuts in the original HP41C. You may have seen one of this: the processor circuit is secured to the main board with metal nuts around the lower screw posts. The problem with these: it is very easy to destroy the thread, since he read was formed by the action of the nut on the first attachment, nearly 40 years ago!

In the later units, the processor was secured in place by the pressure of the back side through two cylinders collated to the case. If you have one of the old cases, and you have broken the nut thread, you need to find a solution to push the circuit down against the zebra connectors. This is such solution. 

We have created a nylon piece that fits tightly around the lower screw posts, with a small bezel to ease the port entrance, and occasionally making a broken post able again. This piece translates the pressure from the back side of the calculator down to the circuit. Don't need to find the right height, or to adjust the angle: it will work - every time.

The piece has sides! As the back side has an angle compared with the circuit surface, we needed to create this angle to the piece. Therefore it can only be put one way.

As the color here really doesn't matter, we have created the price in the cheapest, clearest color from 3D printing: white.

I hope that is piece helps some of you fixing your beloved calculator!

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Zebra connectors for HP

While waiting for the side cover 3D model with a new texture, we have received the samples of another HP41c repair item that has given us a lot of headaches: the zebra connector between the full-nut circuit and the main body. As in many of this things, it is due to the effort of Ignacio Sánchez to find a proper supplier in China. We have received the first shipment and he will throughly test it with a difficult HP41cv. We will report on the results and put it on sale for you DIYers!

The zebra connector has two different models: the initial one, where both sides were united by a plastic membrane, and had good repairability if it wasn't corroded, and the newer "white-green" gummy-like connector. Once it was detached from the circuit, this latter usually didn't work again. This is the one we're aiming to replace.

Stay tuned for news about the first repairs performed with it! We'll post the results here and in

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A new product may be coming...

Most of the HP41c that we receive for conversion are missing the side cover. You can find in ebay side covers but as they are from overseas, they are quite expensive for us Europeans. And you can find some in 3D printing sites, but neither the material quality nor the design makes for a good replacement. So based in our experience with the battery-port assembly 3D printing and with a couple of new materials, we think we may get it right!

Here you can see a rendering of the peice we have designed. We have tried slightly thicker arms, since this is the breaking point, but not too much. We have ordered the first set of samples and we are eager to show you how it looks like in reality!


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The HP10bII+

10bII_Hero_Shot_-_Hi_ResLet's start with the simplest financial calculator from HP. There has been a 10b calculator from a long ago, but the current model is much, much better than the previous versions.

From the innards: this calculator is using the same processor as other fast units like the new 12c. A completely new job by the techs in the HP calculator department.

Also, it has much more functions than the previous versions: a lot of mathematical functions (including trigonometrics and hyperbolics, in a financial calculator) and many financial, including break even analysis. 

The body and keyboard is much better than the competition - the keyboard in particular ranks there with the best, and clearly better than the HP50g or HP30b.

At the price (slightly below 30 EUR) is a steal, and a much better buy than any of the 12C or 17BII units.

The only thing that puts it down for me is the lack of RPN entry method, and the lack of programmability. If you don't need any of these, then it may be your unit!

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Más sobre: HP10bII+
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Financial calculators


Many of us are working in financial positions. I have seen in many offices financial personnel using what in calculator business are called "four banger": just the basic four and typically percentages. In some cases they also have a small printer. This is more than enough in most cases. And in the cases this is not required, you use the Excel spreadsheet - which can also show in a presentable way the results that you are looking for.

The financial calculators are now used in more informal situations: meetings, discussions, workgroups, etc. In that setting, there is still a need for a financial calculator.

We currently sell the follwing financial calculators:

  • HP10bII+
  • HP12C
  • HP12CP
  • HP17BII+

In addition, we typically have the oder HP17BII units from the Pioneer series: a different feeling and a still very valid calculator.

Tomorrow we will describe the different units

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New Product: 4 x back case repair piece!

Some of you guys have several calculators to repair and have asked for a better price if you buy more units. Also we wanted a more convenient way of selling and producing these parts. So we decided to join them and sell them together. You can then cut them by the crosses and use them as individual pieces. Exact length of the cross is not critical.

repair piece

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You can now order the Battery-ports assembly!

Just wanted to tell you guys that I have fixed the article Battery-port assembly. Apparently it was configured with options, but no option was activated and it couldn't be bought!

You can find it here :Módulo conector de baterías y puertos de expansión de las HP-41c/cv/cx

Sorry for the inconveniences of those who wanted to buy it!!

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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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Más sobre: HP41cl
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