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The Bug in Lion's RPN Calculator

I’ve gotten some emails from people complaining about the bugs in Apple’s implementation of RPN in Lion (and previous versions of OS X). The stack doesn’t function the way you’d expect. Let me explain.

Launch Calculator.app and clear all the registers. Enter this simple sequence of keystrokes:

9 ENTER 3 X<>Y

So you started with 9, pushed it on the stack, typed in 3, and swapped x and y. The display now reads 9, with 3 above it.

Now start typing a new number. It replaces 9.

In other words, to make the X<>Y key work correctly, you need to hit ENTER after each use. This shouldn’t be. You can check it on your HP if you want.

I don’t know whether it’s intentional behavior or a mistake. I just made my own RPN calculators rather than wait for Apple to fix theirs (which hasn’t happened since RPN was added to the standard calculator several OS releases ago).

You can get both Full Screen RPN Calculator and Always on Top RPN Calculator from the Mac App Store. They’re only 99 cents. Full Screen RPN works on 10.6, while Always on Top Calculator requires 10.7. Both calculators implement HP RPN faithfully, and have useful features not found in the standard Mac calculator (like full screen mode or always-on-top mode).

Always on Top RPN Calculator for Mac OS X

Full Screen RPN Calculator for Mac OS X

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