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Calculator blog

Musings and comments about our common interest


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Screws for Coconut calculators

image22Lately we're introducing diverse products to help repair for our beloved calculators. 

Most of the repairing needs are about the HP41C family of calculators (code-named Coconut). As you know, we have developed several repair methods for our own repair needs, and we're now marketing it.

What we were missing was feet and lower screws. In the Coconut series, the screws are located below the rubber feet. Initially, calculators were shipped with very short lower screws. This was not important at the beginning: their only use was to close the case's both halves. But later on, HP supressed the nuts that held together the processor and the keyboard, and the pressure required to ensure that the zebra connectors were working passed on to a couple of integrated rings in the back case. These rings were putting pressure on the circuit by means of the lower screws. Therefore, these had henceforth to bear pressure on the thread - and this became a weak point of the calculator. Basically 30% of all calculators needing repair suffer from a problem down below; the biggest defect cause is the corroded battery contact.

HP repaired the calculators putting longer screws. This is still valid even if the post is partially broken - the threads go deeper and the repair holds for longer. Now, the problem was to source these screws.

We have found a reliable source for these screws and we will have in two qualities: stainless steel finish and black finish. For reasons we cannot fathom, the black ones are 9 times more expensive than the others. We will store both for you. 

These are supposed to arrive mid next week and, after some final testing, we will put them in the shop then!! Prices yet to be decided.

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Feet for Coconuts and Voyagers


I have received a lot of feet for the HP41c family and for the HP12c family. Now all repairers will be able to get them for their own calculators. They adhere to the ground much better and look also much nicer. 

Stay tuned for tomorrrow.

There are other products coming - we'll be introducing them as they arrive!


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Card reader repair for HP41c

IMG_0987If you get a card reader now, chances are that it doesn't work. The main reason is the "gummy wheel": the rubber wheel that pulls the card is completely disintegrated into a sticky mess. it is really a disgusting exercise to take it off the axis.

You can see how it looks in the picture besides. It goes away with your fingers - just remember to wash your hands afterwards!

If you are DIY minded, there is a fantastic description of the repair here:

If you're not, or you don't want to get dirty with a messy cleaning (and we won't blame you for that, now we do offer gummy wheel repairs as well, for 30€ plus shipping - please contact us if you need it at for directions.


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screw set for HP41c series

image22We have ordered the production of custom screws to replace the original in your HP41c -should any of them be lost or broken.

In particular, we have decided to change the lower ones for the longer version that was used by HP to repair the calculators when they came back to their service desks. The advantage of these longer scres is that they "bite" deeper in the lower screw posts, saving some calculators where the original screw posts were lightly damaged and did not make enough pressure.

Pressure is not an issue in the newer half-nut machines (those with rounded corners in the screen), but it is of utmost importance in those full nut units that didn't use nuts to screw the main processor to the keyboard, but were pressed to it by means of a couple of stands in the back side. The pressure was produced by the lower screws, and they had to "bite" into the posts, which required be tensioned. This is eased by the longer screws.

In the picture besides you can see a extended lower screw and a higher screw.

We will also provide adhesive silicone rubber feet for the calculator. We're thinking to have a full set of lower screws and all 4 feet as a pack. Upper screws seldom are lost, and those you really need are the lower posts.

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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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