Requirements
I used Microsoft Excel:mac for this. I assume it will work on any previous excel packages, providing they're not too old. i know StarOffice runs it, but apart from that, I have no idea what apps will read it.
for a comp, if you're reading this I reckon you have everything you need.
How to use
Well, if my spreadsheet isn't as simple to use as I thought, then look here. First, look at the table at the bottom and see what units you will use. (I added some more, which won't appear on the other pages, such as the ICBM) Then, work out which is attacking and which isn't. Place the unit name in the right places (cells B3+4). Press F9 and cell C10 will give you a straight answer.
Terms of Use
Not strict, but by law (there must be one) I have to have this here. Basically, don't modify it. Don't claim it as your own piece of work. It is free. You may pass this on, as long as I am mentioned, and as long as it isn't modified in any way, shape of form. I hope that's clear. Good.