Calculator blog

Musings and comments about our common interest


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Old HP calculators and programming quality

HP_15c_Calculator_Hero_hi-res_005Old HP machines!

We’re now in the wake of the new major release of Mac operating system, Yosemite. There will be a number of new features but also correction for many small errors of the previous software. This is typical of today’s software: due to its own complexity, it is bug-ridden, and unsafe in many respects.

Compare that with the 12k * 10 bit of the assembly code of the HP15c. That code was crammed with fantastic mathematical routines that allowed that calculator to perform matrix operations, integrals and solve formulae. Most of the HP15c that have not been physically battered are still working. And talk about battery life. Around 8 pm I receive a 10% battery left message from my phone, while the original HP15c could last up to 15 years with the same battery pack. It could not be upgraded, but there was no need to: it was the ultimate pocket calculator, with everything a science practitioner would ever need, short of a true computer.

Wherever I look into the logic of the HP15c, it seems to me one of the best objects ever designed by mankind. It is the ultimate “less is more” machine. Apart from all keys having three written functions on it, some of them have more: the same key has completely different meanings depending on what you’re doing.

It had 10 digit precision, which was state of the art at the moment for a pocket calculator. Nowadays 14 and 16 digit are normal - however, when in reality you may need short accuracy? And it is not so important the number of digits, but the number of accurate digits. And the HP calculators of that era had absolutely first class algorithms. Most were create by Mr. William Kahan. They were created in machine code, so that it could run as fast as possible with the hp15c hardware.

It used a version of the nut processor (the same as the HP41c), running at an speed that appears ridiculous today: 244 kHz (yes, not MHz), and it took several minutes to perform a 8x8 matrix inversion.

The algorithms were so good that, when HP started the project to reissue the HP15c based on new, modern hardware, they decided to use exactly the same firmware, running on an emulation layer on an Atmel ARM-type processor. There have been several problems in adapting the old firmware to the new hardware - the pause function does not work well, and the low battery indicator does not function in time - at least for me.

But apart from that, it is as good as the original - just 100 times faster!

It is a pity that there are no more stocks of either one!

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More about: hp15c, hp15c LE
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One more HP15c

15c_3smallThere is only one unit left of HP15c. I found a couple of units in the back of the warehouse, and one has been sold already. Beyond this last unit, nothing else, unless HP reissues it, once again.

The concept of a “Special Edition” or “Anniversary Edition” of a calculator is a concept completely strange for anyone outside our hobby. They see the calculator as a fungible item. They don’t understand how a calculator can cost over 10 €, let alone more than 100.

These same guys may wear a watch one or two orders of magnitude more expensive than that 100 € calculator. I tell them, then, “why do you buy an expensive watch? It won’t go faster than the cheapest quartz-driven digital clock. In fact, it will be less accurate and will require higher maintenance.”

Or they write a Mont Blanc, Parker or Omas fountain pen. Leaky (don’t dare to flight with it in your jacket pocket), requiring frequent cleaning and refill, these have some things in common with our beloved calculators: you can use them for your day job, you can have several of them for different occasions, and you derive your pleasure (also) from their handling: the way a fountain pen slips through the page, or the click of an HP41c keyboard when calculating. But, still, they don’t get it.

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More about: hp15c LE
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Two units of HP15C - Limited Edition

While doing an inventory of goods, in the deep end of a drawer, there were 2 boxes of HP15c Limited Edition. New, unopened, with the protective plastic case still sealed...

Once they are gone, never more!

Whoever buys them first, gets them!

This opportunity is reserved first to those within European Union.


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New HP15c LE batch arrived

Yesterday I received the last batch of HP15c Limited Edition. The several boxes of 10 units that I have received have packing dates from 12.4.2012 to 13.4.2012 (European date convention!!). All of them have the initial firmware, i.e. 15.4.2011. This means that in this last release, you will see the same couple of quirks that have affected all units so far.




Quality of keyboard seems, if anything, to have improved over my first unit. And now, when talking about "HP15c Limited Edition", you need to know that the unit I took out of the box had a serial number over 23.000 !! You can imagine that the total production might have been 25.000 units - and that's already a significant percentage of what the original 15c was! (We've been told that over 100.000 units were sold during its original production time - probably up to 150.000 if we count all origins). While 25.000 is a small number when compared with the millions of typical smartphone products, it is already a significant number for a premium calculator.


I hope that someone sees that there are tools that are just "good enough", and don't need to be changed every couple of years for the next best thing. The HP15c is one of them, and deserves to be a part of the HP calculator line, not as a Limited Edition but on its own right.


By the way, many think that the HP42s deserves similar position - but its reissue is much more unlikely, given the development means available and the size of the assignment - unless they take the work of significant members of our community to go faster. For now, let's rejoice in our luck and enjoy the HP15c LE. We do not know if we're going to have it for a long time. I will stop sales when I have just 10 left - and that'll be enough for myself and my children.

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Why using a handheld calculator nowadays - part II

The Smartphone as an alternative to the calculator


If you have a smartphone, then you already have a calculator - or should I say, all calculators.  Due to my job, I use a Blackberry, and the "app ecosystem" is not as rich as that of the iPhone/Ipad. I know that there are a couple of emulators for HP12c, but what's the point of loading one in such small screen, when I have several units of the original machine? But if you have and iPhone, then there is a very wide choice for you - free and payable.

The advantages of a smartphone as a calculator are several:

▪   You can have many calculators - you are not limited to one. There are emulators for practically all the calculators we love. And these are not exclusive: you can have as many as you want in your phone. In fact, calculator apps are not specially big: take into account that most of the original calculators were fitting their logic into 4 kbytes ROMs, or 8 in the case of HP15c, or even 48 kbytes in the case of the HP85a). There are not fancy graphics or memory-consuming animations.

▪   You can have the calculator with all the options - not just 4 modules to choose. There are examples of HP41c smartphone applications, that are running an emulation of the nut processor and can load any of the hundreds of modules developed for that machine; or you can have much more memory than the original; or you can have an extended character set, or more legible number fonts.

▪   The calculator is a couple of orders of magnitude faster than any of the originals, and sometimes faster than even the new models.

▪   You can even carry the manual with you - if you are able to read a pdf in such a small display!

▪   When you hear the click of the key, then it has registered. It won’t happen what we’re seeing more and more in new calculators: tactile positive feedback, and key not registered.

▪   Sometimes we forget this one: you don't need to carry an additional machine, and you’re taking the smartphone with you anyway!

▪   You can upload programs – something your calculator most likely can’t.

However, there are as well some disadvantages:

▪   You can't calculate when you are making a phone call - a situation that, if you look at it, is happening all the time. By extension, you can’t see a contact, you can’t connect to the internet, etc., when you’re calling (unless you’re using a Bluetooth headset, a reader pointed to me ;-), but even in that case, it is cumbersome to navigate the apps while you’re talking)

▪   Usually the screen is much smaller than that of the original calculator. This makes keying in cumbersome, and a high wrong key rate.

▪   Depending on the models, the graphical interface is not fast enough to keep you “connected” to the machine, even though your programs run at breakneck pace;

▪   At a test,

▪       You are not allowed to have a switched-on phone (or a device that can handle the whole library, or access to internet, or…)

▪       You want a dependable calculation device: you don’t want it to run out of batteries during the examination! 

In a way, it is a little bit like using your Iphone as a sound meter – it works, and it works well; but if you’re a professional, you want something specific – and better, for sound measurement.

At the end, the user has the right answers for himself. Myself, I lived a couple of years without calculator when my HP17bII died – and I survived in business without.



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The DM-15cc HP15c clone arrived

As a calculator enthusiast, I could not avoid buying the new kid on the block: the smallish DM-15cc from 

At the very low price of 50 CHF, it is a luxuty one can afford. I bought two units - one to keep original and another to experiment with.

It is based on the original HP15c firmware, running on a nut processor emulation on a LPC1114 ARM processor. The unit chosen should give a decent battery life - let's see. (Not that I am unhappy in any way with the HP15c Limited Edition battery life - after 6 months of heavy use (but not running long programs) it is still using the inital battery set)

The unit is really minimal: see pictures comparing it with the original 15c and the new Limited Edition. I can imagine that it is too small for some fingers, but not for mine.


The keyboard has small domes. Of the two units that I have, on one of them all keys register when they click; on the other, some rows require higher presurre to register. The key feel is excellent, while no one would exchange his old HP for this one for the rest of your life.

The colours chosen mimic more the original than the new. The new is all black, while the original had black keys and dark brown for the surface. This clone has a lighter shade of brown than the original but it makes clear what is a key and what's not.

The keyboard will resist grease and dirt. The unit is not water-proof, though: water can come through the sides since it is not sealed. Here there is a picture of the side. Some dust can make it to the screen due to the same fact.

The calculator can be easily opened and cleaned, though. This is clearly a calculator for the Do-it-yourselver.

The version I have is the so-called version 2. There is a third version coming, that will have an aluminium back and better isolation. I will order another - probably in HP16c form. This version comes with a fiber pouch, but sometimes there is a problem with static electricity, whereas the calculator resets. I have read about it in forums and have experienced myself just once. I guess that it has something to do with the screws in the back. It seems that it will be solved with the newer back in version 3. another short term alternative is to use a different pouch or isolate the screws.


The screen has low visibility under heavy light. This picture was taken on a very sunny floor. but the calculator was switched on, showing "PI". Here below you will see the original on the exact same condition, as well as the LE:


(See the brownish tint to the keyboard surface? Guess you never noticed until you saw the Limited Edition version)


The light conditons make all the more apparent any dust on the surfaces.

The better visibility comes with the original one; second comes the LE and distant third the DM-15cc

On normal conditions, the numbers are much bigger on the DM-15cc. It has two dispay modes: one with rounded digits and another with square ones (mimicking old led displays)

Blog ideas are getting accumulated, and I owe a lot of posts about getting deep into other products. Again, I need to come back to this one. I will put in all my programs and see how it compares with the original, when it comes to real world usability. As well, I will introduce in one of my samples the other firmwares, the ones sporting more memory. 

While I started my professional life as a programmer, I am in no way expert on low level programming. I would like to be able to apply the patched firmwares to one of my HP15c LEs and have a supercalculator. I know it can be made, and eventually I will be able to do it - either myself or somebody else.

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HP15c Warranty repairs

One of our customers made use of the warranty for the HP15c Limited Edition. He just contacted us about his experience. 

The problem he had on his calculator was a small damage on the front panel, just above the x key. I have included his picture - better one image than 1000 words. As he is a collector (as yours truly and many of our other esteemed customers), it was bad enough for him to be upset. He already had other 2 hp15c LE's, but these were intended for relatives.

He called the Spanish Calculator Support team (there are support teams for many countries - later I will post the addresses and telephone numbers somewhere in our website), and he was sent a new calculator packed in bubble wrap in just 5 days.

I would have guessed that it would take a lot of time for the HP15c to reach the support channel - we have been waiting for it for a long time ourselves.

In addition, he has been told that, if he's not contacted by HP in 10 days, he will likely be able to keep the (functionally 100% working) defective calculator.

Talk about service!!

(Additional note: I am seeing in the fori I attend a lot of badmouthing on the HP15c LE. I respectfully 100% disagree. The packaging is first rate, the key click is as good if not better than any other current HP calculator (and on par with the HP17bII), and it is competitive with the feel of the original one (softer, shorter travel distance, but can be seen as mushy sometimes). The speed...well, it makes the HP15c attractive for tasks you would not dream to run with the original model (unless you think that waiting 1 minute for a result is acceptable nowadays)

There may have been some initial quality problems, and some bugs related to the adaptation of the original firmware to a completely new hardware. However, the new model is retrofittable, which the original was not. The bugs are very minor and far apart, and I had not used the feature that causes it in all my life with the original model.

This calculator has been a labour of love of the HP calculator team. You guys asked for it - they took the smallest opportunity they had to find a way to produce it. With the kind of response they are receiving, I don't think they look forward to make another favour to the calculator lovers. If I were them, we all should be forgetting about the HP42s reissue...

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More news on the HP15c...

The HP15c is still going strong but until further notice, there are only 105 units left. Basically 90% of the turnover of the last month belongs to this calculator model. 


In the past, there were huge libraries of programs for the HP41c, but very limited for the HP15c. I encourage you to send us files and we will re-create such library in our website


There are some new developments in the emulator area - in particular related to the HP15c. As we're testing beta versions, we will not show them yet; but here's an screenshot. It will allow to import programs written in text, so that will be the way of storing them in our database.


As a Mac user, I was disappointed that HP did not provide a copy of it in the HP15c package. I have it installed on my Parallel's Windows emulation, but I wanted to have it native as well.




There is still some work to be done on the appearance side - while so far I was not able to detect any bug (Not that I have been testing thoroughly)

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HP15c finally arrived to our warehouse

Dear customers,

The HP15c arrived to the warehouse last week and this Monday the first units were shipped to our customers. Please allow some days for the units to arrive to your homes!

I have received feedback from some Spanish and German customers that have already received their units. All of them (for the sake of clarity) have the same firmware as the previous "American" batch: 2011-4-15.




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First appearance on print of TheCalculatorStore

I received some days ago a mail from Japan, asking me if I intended to sell there, and making strange references to a T3 ad. I have never made any ad anywhere, except from google ads; so it was strange to me. 

Some time later I flew to Lisbon, and got a complimentary copy of the latest issue of T3, in Portuguese. Here is what I found, and imagine my surprise. I guess that the HP15c LE will be of higher interest for these folks!


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