It's all the same. That's one of the funny things about comparing THAC0 and BAB and all that. They're all just different ways of doing the exact same thing.<br/><br/>You can convert one to the other with usually no more than one operation.<br/><br/>For example, to convert Godbound to classic THAC0, simply subtract your total attack bonus from 20. That's your THAC0.<br/><br/>To convert to 3rd edition style AC, simply subtract their AC from 20. That's their 3rd ed armor class.<br/><br/>Both operations also work in reverse. Its all just different ways of looking at the same basic function.