My Android telephone uses the brilliant RealCalc. Never seen anything better for electronic engineers. I hate using PC based calculators. Bloody annoying using a computer keyboard, especially when you have to do many quick calculations or conversions in a day... "click, click, type, click, type, click click"... for heaven's sake.
If you have an Android based telephone, try installing RealCalc. If you love it, pay the couple of dollars for the full featured RealCalc like RPN, orientation mode etc.