PCalc is good. If you use RPN you may want to check out RPN Calc from James Mattis. James has a long history of coding HP emulators for smart devices. I have both and prefer RPN Calc for the iWatch. Unlike PCalc all of the basic functions are on the main screen. The tip calculations included with PCalc I can do in my head. RPN Calcs unit conversions are available on the watch, very handy. For RPN on the iPhone or iPad, i41cx+ rules.