HP35s Scientific Calculator (RPN)

Author's note:

*Although this article is dated, first written in 2009, I smiled today as I reviewed it and decided to re-publish it. I am still using these same calculators!*

This is a digression from the usual computer topics. If you have the need to calculate more than simply adding and multiplying numbers, consider using an HP "RPN" calculator. In this short article, I will explain why this type of calculator is better than a standard "Algebraic" calculator.

To begin, consider this relatively simple formula. Get your current calculator and compute the result:

Questions:

- Did you get the right answer the first time?
- Did you need to write down intermediate answers?
- Did you have to type a bunch of parenthesis?
- Were you confident, as you entered the numbers, that you were on the right track or did you have to wait for the final equal-sign before you were done?

Now try this formula:

Again, the same questions:

- Were you confident?
- Did you see the intermediate results?
- Did you have to save values into Memory (M1), (M2)?
- Did you have to type a boat-load of parenthesis?

My daughter, with her expensive TI calculator, had to try these formulas several times and she was never confident the problem was solved correctly.

Here is the surprise:

With an HP (RPN) calculator, you would get the correct answer the first time. You would have a high degree of confidence, knowing each intermediate step was reasonable -- with results displayed as you type formulas.

For example, on the HP, you would see the following:

- As you typed "2+3" you would see "5"

- As you typed "4+5" you would see "9"

- and when multiplied together (2+3) x (4+5) you would see "45"

Seeing intermediate results is only possible on an RPN calculator. You do not need parenthesis and you will not need to save values to memory.

What is RPN?

RPN stands for Reverse Polish Notation. The gist is this: You enter the formulas in the same way you would if solving on paper and pencil; solving from left-to-right, inner-parenthesis first, using "My Dear Aunt Sally" (multiplication and division before addition and subtraction). These are the same rules learned in 3rd-grade.

RPN keystrokes are different than an algebraic calculator. With RPN, you press ENTER to separate one number from the next and then type the function (add, subtract, etc.) after the second number. Of interest, there is no "Equal" key.

This works to your advantage. With this, you can type the most horrendous function and never once have to type a parenthesis or save an intermediate value to memory.

Using the first example, the keystrokes would be this:

2 (Enter, separates this first number from the second)

3 +

The calculator shows the intermediate result: 5

4 (Enter, separates this from the above "5" *)

5 +

The calculator shows the intermediate result: 9

x (times)

The calculator shows: 45

Sqrt

The calculator shows the intermediate result: 6.708

Without pressing any other keys, begin the second part of the equation by typing:

6 (Enter *Technically, this ENTER is not required because the SQRT resolved)

7 + .... etc.

completing this part the same as the first.

Once completed, press "+", adding the two big sections together.

At each stage, intermediate results are always displayed. Yes, the keystrokes are counter-intuitive, but after practicing for ten minutes, you will never forget and you will never go back. I've used HP's RPN now for so many years, I can no longer use a "standard" calculator and I am embarrassed when forced to -- I can only solve the simplest equations on those types of calculators -- Algebraic calculators now seem completely foreign to me.

Choosing an HP Calculator:

- HP makes both Algebraic (press "Equals) and RPN calculators (press "Enter") -- be sure to pick the right model.

Scientific/Non-business Calculators:

HP33s ($40.00) If you can, buy the 35s; it has a better keyboard.

HP35s ($60.00) Recommended

HP50g ($150.00) Graphing

Business: (Interest/PMT/Financial)

HP12C ($70)

This is an Industry Standard calculator for all financial users. HP reviewed this calculator a few years ago and decided, even after 30 years of production, nothing needed changed. This same calculator, with the same features, has been produced since then. Remarkable.

Look and Feel:

These calculator are pleasurable to use. The buttons "feel" substantial; with a solid, satisfying 'click' as you type. People who use HP calculators rave about the keyboard -- it is unlike any other calculator. When HP has made some cheaper models, with cheaper keyboards (the 33s, for example), users complained.

I believe all of the scientific calculators are programmable (you can write your own functions, automating common tasks).

The other thing about these calculators is they never die. My first HP11c is now something like 25 years old and I still use it several times a week. I think I've changed the batteries twice in 25 years. It uses standard watch batteries.

My other HP calculator, which sits at home, is a 15-year-old HP32s and I only recently replaced it with a newer 35s for no other reason than I wanted to see what the new calculators looked like.

In short: If you are in school, or if you need to do a bit more than common math, spend a few dollars, get a quality calculator. Take 20 minutes studying the first couple of chapters in the manual, and you will never go back to those old, stinky, run-of-the-mill calculators again.