Calculator Pro for iPad, released October 26, has some minor problems. One is with the display and others are mathematical.
The first issue I found is that even with the iPad Region Format (Setings -> General) of “United States,” the app wants to use a comma instead of a decimal point for U.S. usage. The developer is looking into that. (See the screen shot below.)
Landscape format (a simpler calculator is shown in portrait mode)
Next, the developer told me that there is an RPN mode, but there really isn’t one in the manner we expect. More serious is the calculation of factorial for non-integer numbers (which really casts one into the Gamma function.) Calculator Pro gives the wrong answer compared to many other calculators I tested, both physical calculators from Hewlett-Packard and iPad/iPhone calculators, like PCalc and the HP-15C emulator. The developer is also looking into that problem. Also of concern is binary round off. If you calculate a/b and then multiply the result by b, you should get “a” back, even when using binary arithmetic. PCalc handles that nicely; Calculator Pro does not.
For now, I’d avoid Calculator Pro until the developer makes some fixes and publishes an update.