How to determine and adjust centerline thrust?

run it through water and look at the track...I see old beater vans that the rear track is an entire tire width off the front track, funny as heck drving behind one. The laser measurement assumes the rear is centered, which is not the case in mine as I got a tad more clearance on one side. Another way would be to take a laser 90 degrees off the rim to a point a measured ways away and then off the centerline or somewhere that is parallel with the body line up front. Measure between the dots, than take the same off the other side. The distance should be equal if the rear track is square, itll be off if its not, the more distance you take the reading off, the more exagerated the angle will be. Buddy has a cool laser that projects a +, set that up in front down the center and then you got your centerline and reference points out in space.