A generous reader gave me a good tip for answering some questions. I used the money and bought myself an HP 12C Platinum calculator.

This is a financial calculator. It has financial functions like loan payments and bond prices. What really makes it different from all other calculators is that it uses a different input method called Reverse Polish Notation (RPN). In RPN, you enter the numbers before you enter the operator. A normal (“algebraic”) calculation for 5 * 4 – 3 = 17 is entered as

5 [enter] 4 * 3 –

I first saw the classic version of this calculator many years ago from the manager for my first job out of college. When he handed me his beat-up calculator, I didn’t know how to use it. It was just weird. He swore by it though. He said it was the only proper way to do it. It’s sort of like driving a stick shift. People who drive a stick shift love it. They also say it’s the only proper way to drive a car. I don’t know how to drive a stick shift either. While I can’t afford to play with a stick shift, now I can at least play with this weird calculator and see what the fuss is about.

Some of you reading this probably also have a RPN calculator. Do you swear by it too? Do you think I will be converted once I get the hang of it?

thad says

The hp12c is very popular with (older) engineers that I’ve worked with… I’ve always wanted one, but didn’t really think it was worth buying a new one, when my TI 36 solar calculator was only about $10 or $15, and never needs batteries. I suppose if you did enough financial calculations on a calculator it might be nice, but I just use excel for that. Are you familiar with the RPN? It takes a while to get used to it… I used the HP12c for a summer surveying job and that’s what we used the entire time. They are fun.

Wm Tanksley says

RPN is very addictive. It’s nice to get away from the need to pre-plan your expressions and parentheses; you can just enter the operations as you think of them. You do have to learn it, but it’s quick enough to start using, and after a while of consistent use it’ll become natural-feeling.

I do prefer the calculators with larger displays, so that I can see more of the stack… But the 12C is probably as good as it gets for financial calculations. Well, if you can handle a TON of complication, all the recent HP calculators will do as well, but they can handle anything.

Pablo says

I’ve had a 12c (the original, pre-platinum edition) since 1985. I’ve changed the batteries twice, and, it still runs like a champ. Once you get hooked on RPN, I doubt you’ll want to go back.

If you haven’t seen Errold Moody’s 12c page, you owe it to yourself to check out: http://www.efmoody.com/hp12c.html.

Warner says

You will be converted. I was initiated into this cult in late 2006 and I can’t imagine not using it. I was a BA II Plus disciple before but I’ve found the 12c is a much more useful “pocket” calculator.

Ducks says

My dad swears by his. He ran a successful business for 25 years with it by his side. Dad recently bought my husband one, but it confuses him.

Thanks for the link to the Tutorial, Pablo. I’ll have my husband add it to his bookmarks.

Jonathan says

My dad loves his RPN HP as well.

My generation’s geektool was the TI-85. Mine 1996 classic just broke last month. =(

zanon says

I love mine. I had an older model, and my dad an even older one. The manual dated back to the 70s. It really is the best.

anonymous says

I got my first RPN calculator (HP 48sx) in 1992 while in high school. I still have it, and use it daily. This was about the end of the line for RPN among the younger generation, because TI came out with their graphing calculator which was cheaper and had less of a learning curve.

Computer scientists recognize and love RPN right away. A “stack” is a very intuitive way to think about problems.

Everyone else finds it confusing. I have no problem using regular calculators for simple stuff, but anything more involved is better done using RPN.

Don says

Yes, I’m an RPN junkie. I had a HP-41c and then an HP-28s. You can always calculate with fewer or equal numbers of keystrokes with RPN than on an infix calculator because there is no need for parentheses. It is even better if you consider that you have to “shift” for parentheses on some calculators.

Infix:

(5 + 3*8)/(10-1) enter

RPN:

5 enter

3 enter

8

*

+

10 enter

1

–

/

Harry Sit says

Thank you all for the great comments. I look forward to getting hooked on RPN and HP 12C. Maybe one day I will learn how to drive a stick shift too. I’m a really bad driver.

POP says

Do we really need this in the age of MSEXCEL and other free spreadsheet programs.It is probably a nice toy for those who want to have fun but do you need it if you have a spreadsheet as all the calculations can be done using formulas ?

Pablo says

“Need” is a subjective term. The 12c has such a cult following that there is a Windows Applet (emulator) for the 12c: http://mxcalc-12c-rpn-financial-calculator-ppc.3gr-technologies.qarchive.org/

Ted says

I had an HP48 in college. These type of calculators were indispensable for engineering students back when. I have no idea what they use now. They probably do everything on a laptop now.

http://en.wikipedia.org/wiki/HP-48_series

Mary Lew says

I too am hooked on the 12C. Had the orginal, and then was thrilled to get the Platinum version. The really nice thing with the Platinum version is that you can toggle the RPN with Algebraic (that is, “normal”) entry. Sometimes Algebraic is just easier for me for quick calculations, although I appreciate and understand the streamlined beauty of RPN. I am happy to now have both on the same calculator.

And in response to the “why have this if we have computers” I agree computers are great for these types of calcuations, but sometimes there isn’t one available or convenient. I can carry this in my pocket or briefcase.

jimslade says

I’ve used RPN for almost 20 years now… i have two 42S’s (got an engineering degree). If anyone has a spare 12c they’d like to trade for a 42s…

Ben M says

TFB, can you say why you chose the “Platinum” version over the plain jane gold one?

Amazon had the gold version as a lightning deal last Thursday, I think, for $54. I bought it then. I’m still looking for an “antique” one on eBay.

Harry Sit says

Ben – I bought the Platinum version only because refurbs were available on eBay. The refurb I got for $40 looked just like new.

Stephanie says

When I graduated college in 2002, an advisor from the engineering dept gave me an HP12c for a gift. As a business major that survived using a Ti85, I had no idea how to use that thing. However, the HP12c was the best gift I received and by far the best financial calculator. The batteries have gone out and I’m trying to find some where to go to replace it. If anyone has suggestions, please respond.

Harry Sit says

Stephanie – There is a battery door on the back of my calculator. You just slide it off. See page 194 of the user’s guide. It uses a CR2032 coin battery. Most grocery stores and office supply stores sell the battery for $2 or $3.

Tom Peng says

The HP12C is quite an addictive calculator. I recommend it.

thad (my2fish) says

You can now also get an HP calculator application for the iPhone.

http://www.macworld.com/article/141364/2009/06/hpcalcapps.html

Fred Brennion says

I’ve used an HP-12c for years. I have 3 of them, one for the kitchen, one for the dining room and one for the den. I love RPN. I tried to convert a friend of mine who is a real rocket scientist, and somewhat OCD, to use RPN.

No luck. He still, to this very day, prefers to use an old Radio Shack Pocket Computer PC-1 which was Introduced in July 1980.

( http://www.oldcomputers.net/trs80pc1.html )

I have come to realize the validity of his position. When you’re entering a lot of terms and doing multiple numeric operations to yield an answer, You have some idea of the answer that you’re looking for . But if the answer surprises you, then you have to suspect you might have messed up along the way. With the HP 12C all you can do is redo the whole thing from the beginning and pay very close attention. With the Radio Shack PC-1 you can recall the entire expression, and scroll through the entire expression even if that thing is 75 characters wide, and you can see where you put the parentheses and see if the values and order of operations were entered correctly. I sort of see his point; he deals with the vastly more formula complexity than I do.