thanx alot....i knew there had to be a scientifical mathmatical way to do it.......now....to decide one can or 2.........i should probably go with 2 just incase the guy runs out....does goex BP have a shelf life or anything?? i wouldnt keep it very long.....if i bought it in a week or 2 id use it by next fall.......will it be good?? thanx