I have downloaded (and bought) many iPhone calculators and PCalc is by far the best. The depth and breadth of this app is a true labor of love by the author who has spend decades perfecting it (see his website). As an RPN lover and HP calculator addict, I have searched for and tried most of the offerings in the app store only to be disapointed by the rediculous skeuomorphic designs that abound.With PCalc, the amount of custimization possibilities is dizzyingly vast but, once the shock of available options wears off, you are rewarded with a true sense of empowerment. Case in point: I love the elegance and simplicity of the original HP35 from 1972. I was able to duplicate this keyboard layout and, with the appropriate theme, I was able get it looking very nice. This took me a while but my layout is automatically saved to iCloud where it syncs with my other iOS devices.The layout customization is very sophisticated, allowing you to have keys that are hidden until the 2nd key is pressed. All the labels for each key can be set to whatever you want. I'll stop here not because there is not more to say, but because this calculator shines once you start exploring the many options available. The point being, if you don't like what you see in the default layouts, you can make it be anything you want it to be.