Algodoo

Use
Q and A for adding/ substracting 1 from the first number
W and S for -||- the second number
and to change between + | - you use the keys
+ and
´[button on left side of +]
To change between Multiplying and dividing,
X for mult, Z for divide...
Enter button to calculate
I'm open for any ideas on how to improve:D
Edit - added more functions!