Back in October of 2005, I enthusiastically reviewed PCalc 3, which has since been my favorite calculator for the Mac. The developer, TLA Systems, recently released the US$10 PCalc for the iPhone and iPod touch, and it's similarly slick. Although Apple updated the iPhone's built-in calculator app considerably with the release of the iPhone 2.0 software--most notably by adding a landscape-mode scientific layout--PCalc is an appealing alternative, offering a compelling combination of advanced functions, useful conversion and constant features, and a great interface.

PCalc's standard (vertical) mode offers all the functions of the iPhone's own standard-calculator mode, plus percentage, parentheses for nested operations, inverse, square root, exponents, and more. Like Apple's calculator, rotating your iPhone gives you a landscape mode with more-advanced scientific and programmers' features. PCalc includes every function of Apple's calculator except for a random-number generator, while adding features such as decimal, hexadecimal, octal, and binary modes, as well as a good number of additional mathematical functions.

But PCalc's advantages go beyond having more buttons. Near and dear to my geek heart is RPN (Reverse Polish Notation) entry mode. There's also a virtual tape, which displays a time-stamped record of your calculations, and a register (called Stack in RPN mode), which displays both memory contents and decimal-, hex-, octal-, and binary-base versions of the current number. You can even email the contents of the tape or register.

Available in both portrait and landscape modes are two other unique features. Tapping the A->B button (or double-tapping the "LCD") brings up PCalc's conversion mode, which lets you convert the current number--the one displayed in PCalc's LCD--using one of over 80 conversion functions that cover length, power, weight, energy, and more. (Tapping the converted value enters it for further calculation.) Tapping the 42 button lets you choose from among a slew of constants across several categories: astronomical, atomic, electromagnetic, mathematical, physicochemical, and universal. Choosing a constant inputs it for use in the current calculation. And, yes, 42 is the constant for Ultimate Answer.

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