You'd think that a smartphone would come at least with a decent calculator to do the most basic math. Not so with the S60 OS my Nokia E61 came with. Its calculator application is completely useless. Just imagine having a phone with a complete alphanumeric keyboard in whose calculator application you have to choose arithmetic operators by hopping over the displayed buttons with the joystick.
Fortunately, I found an alternative on Volker Weber's blog. Calcium is a nice little calculator application. You choose the operator with the joystick, too -- but just by moving it one in one direction. As displayed on the Calcium homepage, every joystick direction is one operation. And if you want the result, you just press the joystick.
So, even if you don't have an S60 phone with a full keyboard, Calcium makes simple math simple.