While working with the calculator you'll see it shows both sides of the current binary operation. Sounds complicated? See the following example:
1) type 200 + 20 (you'll see exactly "200 + 10" on screen)
2) Click " % " key:
3) The tool will now calculate 10% of 200:
(you'll notice that when you click some unary operation button (%, sqare root etc.), it will be performed on the second operand (in our example - "10"))
3) press Enter key (or click " = ") to get the result
4) Now you will see the final sum:
Just remember - if you want to perform next operation on the result of the previous, click " = " first, otherwise you'll change only the last operand entered. (The only exception is "%=" button - see "percentages" for more on this)
You can use the obvious keys: number keys, dot (floating point), +, -, *, /, Enter (=), ESC (C) and BackSpace.
The advanced ("scientific") functions are not yet accessible from keyboard shortcuts (but better keyboard support is planned for the next release).