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 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.

Consider this formula. Using your current calculator, compute the result:

Questions:

- Did you get the right answer the first time?
- Did you write down intermediate answers?
- Did you type 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 type a boat-load of parenthesis?

My daughter, with her expensive TI calculator, tried these formulas several times and was not confident in her results.

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"

RPN calculators show intermediate results and there are no parenthesis, nor do you need to store values in "M" (memory) -- the calculator handles all of this for you.

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 type the first number,then press ENTER and type the second number. After the two numbers are typed, press the function (add, subtract, etc.) 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.

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 have used HP's RPN 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) low-end calculator.

If you can, buy the 35s; it has a better keyboard.

HP35s ($60.00) Recommended

HP50g ($150.00) Graphing (now dated)

HPG8X92AA (graphic) I will be buying this calculator next:

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 approaching 30 years old and I still use it several times a week. I think I've changed the batteries three times in all those years. It uses standard watch batteries.

My other HP calculator, which sits at home, is a 20-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 twenty 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.