I have been using HP calculators, and so must be many of the people who are looking for RPN calculators on Mac OSX. Therefore, one of the criterias for the star ratings below is based on how close the calculators behave as HP calculators. In addition, the calculators should have basic keyboard shortcuts for a quick entry. HP calculators had keys, not mice.

There are mainly two kinds of reverse polish styles, RPN and RPL.

With RPN, the number you enter goes into the bottom of the stack (x-register for HP calculators). The "ENTER" key copies the contents of the x-register into the next y-register. HP calculators like HP35, HP25, HP15, HP32S, HP42S, etc. fall into this category.

With RPL, the number you enter goes into an input buffer first. The "ENTER" key copies the contents of the input buffer into x-register. You can also enter a number followed by an operator. For example, 2+ adds 2 to x-register. 2 sin pushes sin(2) in x-register. HP48 falls into this category.

If you are familiar with old HP calculators using RPN, you might get confused a little with RPL. For example, to calculate 2 + sin(2), in RPN, you do 2 ENTER sin + because you will have '2' in both x and y registers after hitting ENTER. In RPL, this is not the case, so you have to do 2 ENTER ENTER sin +.

For more details, take a look at Museum of HP calculators.

RPN calculator

- Well thought-out keyboard shortcuts allow you to calculate without using a mouse.
- Very powerful, and has many functions.
- Handles complex numbers and functions.
- Standard/Scientific/Engineering display modes are available.
- It occupies small area on the desk top. With extensive keyboard shortcuts, it can work even without showing keys.

- Cannot enter octal/hexadecimal numbers directly. (But I will forgive this).

A normal looking calculator turns into RPN mode by selecting the option.

- It has three modes, basic, scientific, and programmer.
- Programmer mode has unusual "Byte Flip" and "Word Flip" buttons.

- Keyboard shortcuts are limited.
- It cannot swap x and y registers.

- 4.0 had a serioius bug; Typing "C 1 EE 0 enter" caused an error, but it is fixed on v4.0.4 that came with OS X 10.3.4.

RPL calculator. This uses the code in HP48GX ROM.

- Works exactly as HP48GX.

- On PowerBook G4 (800MHz), the "+", "-" and "*" keys do not work as keyboard shortcuts.
- Not many keyboard shortcuts are available.

This calculator has RPN mode.

- Works almost as HP calculators.
- It handles hex/oct/bin mode and their bitwise logical operators.
- It has many unit converting functions.
- It has drawers for "Info" and "Tape".

- It lacks "Last x" key, but command-z will undo the last operation.
- Keyboard shortcuts are not available for many of the common scienfic functions.
- The function of "Delete" key is confusing. While keying in numbers, it behaves like HP's "< -" key, which deletes the last digit. However, once "ENTER" key is pressed, it behaves differently. For example, on HP calculators, 1 ENTER <- 2 puts 1 in y-register and 2 in x-register. "Delete" key on PCalc drops y-register (01:) to x-register, and replaces 1 with 2. To let PCalc behave as HP calculators, you should press "C" button or its keyboard shortcut, "esc" key.
- Complex number calculation is not as simple as RPN 1.96.

Widget for Tiger. This is an RPL calculator.

- It shows multiple stacks.
- It has descent decent shortcut keys, as "s = sin, shift/s = asin, ...".

- If you enter numbers by both buttons and keyboard, the cursor hangs at a wierd position.
- Invalid input pushes buttons away from the calculator, and sometimes it takes other operations to restore them.

Widget for Tiger

- Can show in fraction format.
- Has hexadecimal, octal formats.

- The accuracy is poor. For example, "0.000001 Enter 1 + 1 -" returns 0, and "89.9 sin asin 90 -" returns 0.
- There is no "E" key to key in in an exponent format like 1.2E3.

Multi-precision RPN calculator.

- The precision can be set to many digits.

- The keyboard shortcuts only correspond to the position of the buttons, instead of their function names.
- It lacks Last-X key.
- Log10 and Ln are on different keypad.
- Even for simple arithmetic, you have to use a mouse. For example, 1 return 2 + does nothing. You have to use "+" button on the panel.

RPL with input buffer.

This is an odd ball. It has no keys. All you see is an entry field and the last 3 levels of stack.

- You type functions, and it is faster than using a mouse.

- "-" is treated both as a prefix for a negative number and a "minus" operator. Therefore, you cannot do "2 ENTER 3 ENTER -" for 2-3, while you can do "2 ENTER 3 ENTER +" for 2+3. (To do this right, you have to do "2 ENTER 3-", or "2 ENTER 3 ENTER sub".)
- Repeating ENTERs does not push the x register into stack. Therefore, to enter the same number, you have to either type in the number again, or use "dup" function.
- It lacks "Last-x" key.

RPL with input buffer

- It has hexadecimal and binary mode.

- The "+/-" key does not work as a unary operator to change sign.

On HP calculators, "+/-" or "CHS" key changes the sign of the x-register. However, f(x) the "+/-" key works only for the input field. This is fatal. - After using for a while, it failed to accept keyboard entries.
- Keyboard shortcuts are less sensible.

O for cos (although S is used for sine), X for ex (although it is displayed "e" on display), = for +/-, etc.. - It accepts decimal point for the "exponent" entry.

You can enter 1e+2.5, which should not be allowed. - It also accepts multiple "ex" (exponent) keys.
- Although it has hexadecimal and binary mode, it does not support logical functions as AND, OR, and NOT.
- It lacks "Last-x" key.

RPL with input buffer.

- Right after "ENTER" is pressed, the following "+" and "-" keys (not buttons) are treated as a part of the next number, instead of an operator. Therefore, although 5 ENTER 2 ENTER * gives 10, 5 ENTER 2 ENTER + does nothing. Therefore, + and - operators are not treated equally as * and / operators. (You have to do 5 ENTER 2 +.)
- Scientific functions are run as a script. Therefore, you have to select it and press "Run" button. This is tedious.
- It lacks "Last-x" key.
- "ENTER" does not push the contents of the x-register into stack. You have to use "Dup" key instead.

RPL with input buffer.

- It has last-x key.

- The "+/-" key is not an unary operator. This is fatal.
- It lacks basic scientific functions.
- It occupies large area on the desktop.

RPL with input buffer.

- It displays an input buffer on entry, and the bottom of the stack after ENTER is pressed. For RPN users, this is more confusing than other RPL calculators which clearly shows an input buffer separately from the stack.
- It lacks scientific functions.
- It lacks LASTX key.
- It lacks the exponent key.
- Delete key drops the last value in the stack.

RPL with input buffer.

It does not even work as a calculator.

- asin, acos, atan return wrong values!
- It does not accept negative exponent.

1 E 2 +/- gives -100, instead of 1E-2. - It lacks "Last x" key.
- Return key is not treated as "Enter".

December 3, 2005, Taku Yamanaka