You really need to roll the truck forward before measuring or have it on alignment plates. The plates (as I call them) have ball bearings under them so the tires float around and the truck will set in its normal drive position. With out tires, or the weight of the truck on the front, you won't get a true reading.
I have also read not to take a reading off the tire side walls in case one might have a lump or something. The scribe line eliminates any deviations of the tire. I double checked mine using a string line from the rear tires to a point will out in front of the truck. With two lines parallel to the rear tires and equal space from each front tire, I could measure the distances and figure the toe-in from the differences.
In reality, any of the ways will get you close, and a test drive will confirm if you need more or less. I believe to much toe out causes a pull to one side or the other, and to little causes a wander and a loose feeling in the wheel.
Joe
