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 the formulas were being typed.

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

- As "2+3" is typed, the calculator would show "5"

- As "4+5" is typed, "9" is displayed

- and when multiplied together (2+3) x (4+5), "45" appears in mid-formula.

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

What is RPN?

RPN stands for Reverse Polish Notation. The gist is this: Enter the formulas in the same way as-if solving with 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, type the first number, then press ENTER. 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. The most horrendous function can be typed and never is a parenthesis or intermediate save needed.

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 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 the second section is completed, press "+", adding the two blocks together.

Results: 21.5743

At each stage, intermediate results are displayed. The keystrokes are counter-intuitive, but after practicing for ten minutes, you will never forget and will never want to 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.

Choosing an HP Calculator:

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

Bankers, investments, and real estate, choose a Financial calculator (12c).

Otherwise, choose the Scientific calculators (even if you are not a scientist).

Here are my recommendations:

Scientific/Non-business Calculators:

HP33s ($40.00) low-end calculator - chicklet keyboard

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 (update: now bought, but not reviewed):

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' when typed. 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 revolted.

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

These calculators 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.