i agree with BD but i know that a lot of people dont adjust their chains that way. i venture to guess that most just adjust it to where they feel it will be ok. when i do mine i take the chain and pull up and down and generally have from about 1.5 to 2 inches of play. then pull down the rear end to see how it looks. may not be a scientific way to do it, but its more than likely the way that most people do it. by the way, im guessing on the amount of play, i was just sittin here with a mental image of when i do it and it sounded about right.