PlusMinus

Fill the empty fields with "+" and "-", so that the result in every row and column is equal to 0.
You can use the mouse and click into a field to change from "+" to "-" or from "-" to "+". You can also use the arrow keys and "+" and "-".

This is a 6 x 6 - problem for profis, beginners should begin with 4 x 4 - problems.