Paste the attacker and defender SOMs into the boxes on the right, enter the attacker and defender's bonuses, and press Submit. The calculator will then tell you how many of the attacker's forces equal the defender's defense, unless the attacker's forces are weaker, in which case the calculator will say that the "attack won't succeed." Use whole numbers instead of decimals (like 25 for 25% and not 0.25). The attack and defense bonus values are the ones you get from your player type or your position within your country. Experiment, and don't forget the difference that research and alert colors can make.