## Guido's RPN calculators |

The algebraic notation as used by most calculators LOOKS simpler. Telling a student "Just type it in as you find it in the textbook" is easier than explaining how RPN works. Have however a look at this interessting experiment that compares calculators with RPN and algebraic notation.

I have been using HP RPN calculators since the beginning of my university years. Now that PCs and Laptops are one every office table I have been looking for a good calculator that just runs independent of the operating system on any computer out there. I did not find one so I wrote one my self. Beginning of 1997 I started to write rpnjcalc. I have used it once in a while but it never really felt like a real HP pocket calculator. I always found my self looking for a real HP pocket calculator when I had to do some calculations. So finally in March 2008 I decided that it must be possible to write a more usable calculator in Javascript and I developed gsrpn. While my calculators work with any old browser (pre 2010) you can find now calculators written for more modern web browsers and they look and work like authentic HP calculators.

- Greg Hewgill's HP-15c: http://hp15c.com/. He has versions for Windows and Mac as well as a java swing version that can be used under linux (run: java -jar HP15C.jar). The java code startup is very slow.

Greg wrote a very authentic javascript based HP-15c [Local copy of the javascript based hp15c]. You can resize the window if you want to see the registers.

- Torsten Manz wrote the best desktop version of the HP-15c: http://hp-15c.homepage.t-online.de. It runs under Windows, Mac and Linux.
- Elvis Pfutzenreuter: https://epxx.co/ctb/ has a number of apps and calculators including a web based HP-15c emulator.

It's interessting that this calculator is "1 * π inch" high and "Φ * π inch" wide (where Φ=1.61803...=(1+sqrt(5))/2 prounouce: phi, Φ is also known as the "golden ratio", π=3.141... prounouce: pi, Φ*π=5.083).

For several month a petition was circulating on the internet to bring back the 15c and it seems HP took notice and produced end of 2011 a "15c Limited Edition", the HP15c-LE. It does not only look similar to the original. It is very much like the original with some small differences. On the down side are a number of firmware faults: hpmuseum.org, list of 15c LE bugs but on the up side is the advantage that the 15c-LE runs faster than the original 15c and it has the same good quality keyboard with an excellent "click".

The list of faults of the HP15c-LE might look long list but the only real problem is the fact that the PSE (pause) function can only be called once per program execution. The non working low battery indicator is pretty bad too but you can just use a voltmeter and test the batteries once in a while as described in my hp15c-le battery test article. There is no need to take the batteries out for testing.

All programs that I have ever written are however not affected by that PSE bug.

It's a bit unfortunate that the HP company of today is not any more the company that took pride in producing high quality measurement equipment and calculators. They have not provided a firmware update until a year later and I don't think they will.

I have investigated the HP15c-le power and battery problems and written about them at http://tuxgraphics.org/npa/hp15c-le-power-test/

www.swissmicros.com (previously known as www.rpn-calc.ch) produces a hp15c compatible calculator. It's emulating the original Voyager processor on new hardware and runs runs original HP15c firmware. The hardware is designed with firmware updates in mind. It has therefore as opposed to the HP15c-LE no software bugs. I like the fact that the color scheme follows the original hp15c. The calculator is roughly the size of a credit card. The keyboard could however be improved a lot. You have to really watch what you type or you have to use a pencil with a soft rubber eraser and type with the rubber end of the pencil. Those rubber eraser tips that you can put onto the end of a pencil give the best results.

The DM-15 HP clone

Swissmicros.com produces since Oct 2015 a new model called DM-15L. That calculator is really the best HP-15C clone that I have seen to this date. The keyboard is much better than the one on their small credit card sized editions. This is a very well designed calculator. The case is super strong, has the same dimensions as the original and weighs approximately the same as the original. The keyboard had initially some issues but they fix them and it works now very well. The keys are flat and not beveled but they to the job well. They keyboard is reliable. I like it a lot. This is a very good and usable calculator.

The Swissmicros DM-15L

The DM-15L has a serial number on the case. I have three DM-15L with the S/N 430, 554 and 532.

The Swissmicros calculators have a few key combinations that are specific to Swissmicros. The most important ones are:

CHS and then ON: change LCD contrast with + or - keys 1/x and then ON: show firmware version and battery voltage Note: 1/X is the key left of CHS and is called E on the DM-16 7 and then ON: change the font 9 and then ON: change clock speed, 48MHz should be the normal speed

The HP15c has a very ergonomic shape allowing for fast typing.

- convert a floating point number into a fraction (numerator and denominator)
- quadratic equation solver, x
^{2}+p*x+q=0 - number conversion dec->binary
- Euclidean algorithm, Greatest Common Divisor (GCD)
- A dice
- Generic unit conversion
- number conversion binary->dec
- Calculate Canadian sales tax (GST/PST)
- Small program to calculate the modulus: Y mod X

- Basic RPN tutorial by Guido Socher
- http://www.hp15c.org/RPNHowTo.php, Christopher Woodhouse's hp15c petition page has a RPN-Howto.
- http://hansklav.home.xs4all.nl/rpn/, Hans Klaver's RPN Tutorial.

3 Enter resulting stack: 3 2 Enter 2 CHS -2 1 1This results in the stack as shown on the right. The -2 is considered "computed" and we get an automatic stack lift when the next number is entered, 1 in this case. If we enter however "0" instead of the two then we get a different behavior.

3 Enter resulting stack: 0 Enter 3 CHS 0 1 1This is the only known bug in the original HP15c and you can work around it by always pressing an extra enter if the number you want to CHS on is already entered or computed. This would keep at least the X and Y registers (bottom two) the same even if there is a zero.

I have long been looking for a good replacement pouch for the 15c. Especially the HP15c-LE pouch is too hard and too sturdy. My old one is on the other hand wearing out and getting too loose. After trying several options I made some pouches out of neoprene and they are really good. If you want one, you can order them here: http://shop.tuxgraphics.org/fan/hp15c-hp12c-pouch.html.

The HP12c has no trigonometric functions but you could use the following approximations if you ever need those functions.

- linuxfocus.org RPN calculator article
- gsrpn -- a HP alike RPN calculator
- http://www.hp-collection.org/
- http://hp15c.com/, online simulator
- http://www.hp42s.com/, everything hp42s
- http://hp-15c.homepage.t-online.de, a hp15c simulator for Windows, Linux and Mac OS X
- http://www.hpmuseum.org/
- http://www.hp.com/calculators/, HP produces again some of the classic RPN calculators.
- http://www.hpcc.org/calculators/hp15.html

© Guido Socher