When run in landscape mode, each app uses the original ROM code and provides an exact visual replica of the actual horizontal-format calculator, making it familiar to users of the originals. The $15 HP 12c and $20 HP 12c Platinum provide the same business-focused functions and formulas as the hardware models, and the $30 HP 15c includes all of the original's scientific algorithms and calculation sequences, including matrix, root, and complex-number functions. All three apps are also, like their hardware counterparts, programmable. (The HP 12c and 12c Platinum are still in production; the HP 15c is no longer made, but used models still command high prices.)
HP has taken advantage of the iPhone and iPod touch's hardware to add functionality. For example, the company has included a vertical calculator interface when the iPhone is rotated. In this mode, you get a simplified version of the calculator that hides many of the advanced features. The HP 12c Platinum app gains the same editing features and algebraic entry, compared to the standard HP 12c, as its hardware counterpart, but also includes a tip calculator in vertical mode. And because the iPhone's hardware is much more powerful than the 4-bit processors on the hardware models, each software calculator is much faster than the original.
The original 12c or 15c calculators also provided useful formulas and references on the back. The company has preserved this popular feature in software: tap on the HP logo on the "front" of the software version and the view rotates to display a faux backside.
The HP 12c and HP 15c should be available on the iTunes App Store today or tomorrow; the HP 12c Platinum is scheduled for release in early August. The company is also releasing similar software calculators for Windows. HP representatives told Macworld that the company is considering bringing other classic models to the iPhone, depending on how well these apps do.
Updated 6/25/09 2:35am: Corrected misstatement about HP 12c Platinum being discontinued. It is still available.