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Calculator blog

Musings and comments about our common interest


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The HP10bII+ - a different animal from previous models

10bII_Hero_Shot_-_Hi_ResThis is the most inexpensive financial calculator from HP. A descendent just in name from several versions of HP10b, it has been thoroughly improved, using all three functions of most keys to give it a much wider range of functions than any other - including many scientific ones. Even trigonometric functions! It also includes a simple solver to perform breakeven calculation - something I have been programming as solver in my HP17bII and HP19bII+ units always!

The feature set is really impressing - as a student you really can't ask for more in a non-scientific calculator. Far, far better than the previous inceptions of the same calculator. You have trigonometrics and hyperbolics, combinations and permutations, many statistic functions including regression, and then Time Value of Money, bonds, breakeven, date functions, cashflow analysis, markup and markdown, etc.

Both screen and keyboard quality are high, and it looks professional too. It is based also on a SOC (system on a chip), of the Atmel family.

It doesn't have RPN, though - its only flaw in our view! Ideal for a gift or as an inexpensive calculator to be at another desk.

The price is 30 € plus shipping.

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A lot of HP17bII+


17bii_1bigWe have received a new lot of HP 17bII+ calculators. They are now priced at a competitive 77,90€

It is true that the sexiest financial calculator is the HP12c, but the HP17bII+ is soo much more powerful.

From the beginning: it is extremely solid. The whole back part is on hard plastic - the beautiful metal front is protected by the raised sides. Keys are big and wide, and click very well. As the machine is menu-driven, the keyboard is not as cluttered as the HP12c or some scientifica calculators'.

It comes with a protective pouch. It is build in the same way as the HP35s, but it is not as big as its scientific sibling.

The screen is two lines but one of them is reserved for the menu hotkeys. This hotkeys can be programmed through the solver application - which is a programming system in itself - and an easy one, at theat.

The menus make it a lot easier to remember how to do things. While with the HP12c you achieve things with less strokes, the HP17bII+ allows you to be able to recall most of the components of the calculation for later use.

When it comes to statistics there is no comparison between both. With the HP12c, with each data pair entry you are feeding the 5 counters (n, x sum, x2 sum, y sum, y2 sum and xy product) but the information as such is not kept. With the HP17bII+ the data is kept in a list that you can save, edit and retrieve for another moment.

Cashflows for DCF calculations are kept in both - but the HP17bII+ makes it much easier to edit them. You can also choose between individual cashflows or grouped cashflows.

The real strong point of this calculator is the solver. You can write any formula algebraically and the system will keep all the variables in the hotkeys, allowing you to solve for any of them. As you can store a lot of formulae, you can really configure the machine for your own uses. Typical formulae include Black and Scholes, trigonometric functions, break even analysis, etc.

There are a lot of scientific functions too - all except trigonometric (but think - when was the last time you used them?)

Some of you ask me several times what are the differences between HP17bII+ and the original HP17BII. Here there are:

  • The new model is a new calculator built on a different processor with different firmware. The old was based on the Saturn processor - the same as the HP71B. The new is based on the 6502.
  • There is a new menu for currency comparisons. It is very useful - provided that there are not huge rate changes.
  • The memory is at least 3 times bigger than the original - useful if you really use the solver and store a lot of formulas.
  • Some very ultra-rare programming solver functions do not work in the new model.
  • The screen contrast and quality is at a completely different level - much better in the new one.
  • Keys are equally nice to use but the newer machine's are bigger.
  • Cosmetically there is the old brown HP colour in the original machine, vs the classy metallic surface of the new.
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IMG_0821We have received a beautiful HP32sII calculator. Just a single scratch under the "3" key. 

Available here:

For 130€, including an excellent vinyl cover.

Please remember also to see our list of HP41c units - now there are 4 of them online.

This is a quite powerful calculator - only second to the HP42s in the Pioneer line. Arguably better than the HP35s in many respects and in particular ease of use. 


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Repair service for HP41C

4e4da4ed-87a5-4e0b-a8c1-0e53b7642c46We have developed a number of techniques to repair HP41c calculators. These include the corroded battery bay, corrosion on the zebras in the full-nut calculators, broken lower posts, broken upper posts and broken back case.

However, we understand that to open a calculator is quite a daring enterprise for most of us - even if we're technically minded, it doesn't mean that we're DIY-inclined.

So we offer a repair service for HP41C, CV and CX calculators. The conditions are as follows:

  • Initial diagnosis is for free - but we may decide that it is non-repairable.
  • If repair is possible, the price is 40€ inclusive of all repair parts, except if a battery bay replacement module is needed, where the total price is 75€.
  • Replacement parts (back port covers, battery bay, side port cover) come in addition at 20% off the list price.
  • Owner pays back and forth shipping, and all import/export taxes.

If you're interested, you can contact us at , and we'll arrange shipping.


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Battery bay repair piece

sketch_moduleThe latest battery piece is used to repair the typical corroded contacts in HP41c calculators. By far this is the most typical repair need in these calculators.

Some years ago, Diego Diaz created a foldable, adhesive circuit that could be used instead of the original cicuit. Initially, you would peel off the original circuit, remove the plastic rivets with a X-acto knife, and paste the new circuit once pre-folded. This was a fantastic solution!

This gave fantastic results - for a while. The adhesive, while strong, would give after several months of use - sometimes up to a couple of years. No matter how it pasted and pre-folded it, after a year of use the adhesive would fail and the outer part of the circuits would peel off. Good for your own calculator, but not good for somebody else's file. 

So we set to find a permanent solution. 

After some thinking, we addressed these failures. We decided to fix both sides with screws, with a total of 8 of them. We use also two 3D printed pieces to fix these circuit ends:

On the right you can see an exploded picture of the part before adding the circuit. This makes sure that it will never peel off! It has also tighter measures than the original, and gets secured by its shape too. We still recommend to put the back ports when closing the calculator, since it pushes the module in place.



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A new Zebra batch has arrived


zebralinWe have just received a new batch of zebra connectors for HP41c. The compound chosen is more flexible than the previous one. The thickness has been optimized to avoid gaps in the lower part of the calculator, while keeping good pressure between both circuits when pressed together.

To do so, we have a central conductive part surrounded by two softer isolating silicone sides.

You can see it in the pictures beside. 

In some cases (depending on you application and what the old zebras were) you may need or not the optional zebra holder.

The price for a pair has been lowered to 6€. 


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Flex circuit installation for the HP41c calculators

We offer two products to repair the frequent corrossion on the battery contacts. The most frequently sold is the complete assembly - it is ready to be put in the HP41c calculators as it comes. This is the version we recommend to our customers.


However, some of them are more adventurous or more daring, and that decide to go the extra mile and assemble it themselves. for them we have the naked Flex circuit. 

However, I'd like to give some comments from my experience of assembling more than 60 units myself:

  • If you paste the circuit onto the original plastic piece, be aware that sooner or later the contacts will peel off the plastic. There is a solution for that: using our set of 3D printed pieces, the circuit is secured mechanically to the support, with fixing pieces and a total of 8 screws per part.
  • You need first to remove the original circuit. You need to use a X-acto type of knife, and remove the rivets that fix the circuit to the plastic. I usually then cut the circuit by the contact area, and use the freed area to grab it and pull out the rest of the circuit.
  • Clean well the plastic piece from the grease that usually can be found inside the calculator. 
  • Pre-fold the flex circuit:
    • On a table, lay the circuit with the contacts side on top and the while paper down, leaving the funnelled part far from you.
    • image6-2
    • Fold upwards and away from you, and create the two bends that will be the part between the four module contact tabs. These folds should coincide with the short sides of the two circuit opening. Do not fold anything else yet.
    • image8-1
    • Turn the circuit face down. You have now the white part facing up.
    •  Partially peel the paper until the second bend. fold it there.
    • image9
    • Start adhering the circuit to the plastic from the extreme, in the side farther from the battery contacts. Ensure adherence everywhere with a non-sharp tool.
    • image10
    • Fold the circuit by hand on the top of the first tab, and push the bent part into the "valley" between both tabs. With the tool, press the bends you did at the beginning against the "corners" of the valley. The white part still adhered to the circuit should have helped you entering the circuit in the "valley". 
    • image11
    • image12
    • Now you can remove the paper altogether. 
    • image13
    • Bendthe circuit over the second set of tabs. Ensure adherence with your tool, and create the next bend.
    • image14
    • Now paste the battery contact part to the small contacts tabs. 
    • image15
    • Paste the rest of the circuit in between
    • image16
    • You have  finished! Now let's ensure it stays put: you can try with memory modules in all four tabs, to make sure the circuit is pressed against the plastic.
    • If you choose all our parts, including the base and the two fixing parts, you can further secure the circuit with a couple of pieces with screws:
    • image17
    • Leave overnight

And you're done!


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Zebras for the HP41c

IMG_2838The HP41C full nut requires two zebra contacts betwen the keyboard circuit and the main processor. The original zebras seldon get destroyed, but in severe corrosion cases, the zebra connectors are also affected. Then you need to change them.

In there were several threads about alternatives for the zebras. We have done something else: we have custom-ordered a couple of zebra connectors that work for our application. The length, width and height are based on the originals. 

Now, the original is two round copper cylingers joined by a plastic membrane. As we don't have this membrane, we have designed a "zebra-holder" that keeps the zebra pair in place. It is made in 3D printed nylon (with a HP printer, of all brands!). It replaces the old structure, so that it can be round the zebras to keep them firmly in place. The old structure can be removed with pliers and a little force. Be careful to avoid breaking the screw posts.

If the screw posts are damaged, broken, or the screw rotates freely in them, the required piece is a different one, the lower post repair, which replaces both the zebra holder and the screw post, and that is glued in place.


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A couple of audio-related products

As some of you know already, my other hobby is audio. And as a frequent voyager, audio means portable audio. 

We have created a couple of 3D pieces for problems that we have found in our portable devices.

We are lovers of the Stax Lambda electrostatic headphones. However, sometimes the side assembly breaks. We have designed a 3D replacement, that you can find in our audio area or in our webshop in eBay. It just plugs into the hole of the headband and allows some rotation on its axis, since it has been designed with the stem printed within the body - this you can only do with 3D printing!


This piece helps solving a problem for many users - I hope! I have found yet no other use for the "print inside" capability of the 3D printers.

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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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