More than 40 years ago I took my Dodge to get an alignment done by well recommend shop. He had the best equipment at the time, yet did the toe-in in a simple way. He jacked each front wheel off the ground, and marked the center with chalk, then used a sharp scribe to make a fine track, at the center of the tire by rotating the wheel. He then used a measuring device to measure between the tracks, rear and front. He also did the T-Bar height, camber and caster too, but that is another story.
Typical alignment specs are 0 to 1/8" toe-in at the front. I find 1/16" works well.
I built a simple adjustable tool using a couple sizes of steel square tubing, an aluminum, two nails, and three set screws. Three brackets were fabricated that side onto the aluminum tube. The brackets fasten in place with set screw. The third bracket serves as a stand. The idea of the tool, is to make consistent measurements, front and rear. If a tape measure is used for measurement it must always be parallel to the ground and at the same height, or the measurement will be off. To use the tool, start with rear of front tires, set the nails to the tire center mark, then move to the front and compare. A 1/16" is the diameter of the nail so it is easy to estimate.
My particular tire tread has an OEM scribe in the center, so I use it.
