I bought my first RPN calculator in 1984 during my freshman year at Clemson University. It was an HP-11C. I don’t remember the reason I chose a RPN calculator. I know I needed an scientific calculator, but RPN (Reverse Polish Notation) was new to me; prior to this purchase, all I had ever used were Casio and TI algebraic calculators. Thinking back on it now, if I had to guess, it was probably the bullet-pointed marketing, or the long equation solved simply example on the box that sold me; but whatever the reason, I clearly remember sitting down in the library, reading the manual, and learning to use this RPN calculator. That first 30 minutes to an hour of playing with this new, strange little calculator (the HP-11C was designed to fit in a front shirt pocket–making it a true pocket calculator) quite literally changed my life!

I know that sounds sort of nerdy, but since that day in 1984 I have not been able to use a non-RPN calculator–at least without difficulty. I won’t make this a tutorial on how to use RPN, but I will say that once you use one, going back is difficult. Using a normal calculator requires more keystrokes, and is not intuitive for me now. Some of the reasons RPN calculators are superior (in my opinion) to algebraic include: error correction; intermediate results are shown; less keystrokes are required; no parenthesis; and the stack.

I’ve owned many RPN calculators since 1984 (and I still have the first one too). My current daily use calculator is the HP 35s. RPN calculators are mostly made by HP, and are hard to find in physical stores (you most often have to buy them online). Fortunately though you can easily install a RPN calculator on your linux computer.

orpie My favorite RPN calculator for linux is orpie. Orpie is probably already in your distro’s repo as well, at least it is for debian. What I love about orpie is that is Curses based and as such can be used in a terminal. Because it is a terminal app, I can run over ssh, i can run without a window manager, and (my favorite way) I can run it in a hot-keyed floating terminal that i can send to the I3 scratchpad and pull it up anytime I need it. Orpie is the main reason I don’t regret buying a laptop with a number pad.

I love HP RPN calculators, and I love orpie too; they make math fun.