What I have done when doing my alignment is the following.

I would set-up my 4 jack stands at the corners with a string on each side parallel to the car. Then I would measure from the hub to the string on wheel. Track is not the same front and rear, but both front wheels would measure 6.5" to the string from hub. I would align the string to be in line with center of hub vertically. Anyway I would do this on the front. The do the rear. Again measure thenm equally in the rear. Not 6.5" this time, but again equal side to side. Then I would check the front and it would tend to shift a little. Over and over gain I would ajust till I got them right. Then I would check the end of string past the car front and rear to make sure strings were parallel. Same distance apart front and rear.

Once this was done I assuemed the two strings were parallel and the car was perfectly centered between the two strings.

Then measuring toe is as easy as measure form the string to the out side of the wheel in two places. Front and rear. This way could measure toe to 1/16 or even guess it to 1/32nd of an inch. Now adjusting was a little harder, but front was pretty easy as I can just reach the tie rods the car on the ground. This way I never need to reset my strings. Rear was more complicated as my initial measurment would tell me where I was and then I woudl calcuate how much I needed to adjust. So I tend to shoot for 1/16 toe in per rear wheel. So I could determine where I was before adjustment and then calcuated per rear wheel how much I needed to move it. 1/16 or 1/8 out or in. I would also take note of rear camber too and record it.

Then I jack up the car just enough to free the rear wheel. I would then measure camber again. This number was not an accurate camber, but represented in droop state what every loaded camber I had.

So then remove the rear wheel and I would measure from the brake caliper fixed point on the inner fender. From here I would record the distance and I would make my toe adjustment. 1/8 short dimensino or 1/16 longer. I would make these adjustments till I got change I figured I need from my on the ground wheel measurement. Then I would put the wheel back on and check camber again in the air. Again see how much this needed to change to get what I really wanted. I would do this again on the other side and was careful to take my initial measurements to the string before I jacked up the opposite side.

Anyway once I finished it in the air I would lower the car and put the rear wheels on slip plates I made from a gallong zip loc bag with dish soap in it. This minimized the binding. I would then recheck that the car was aligned in the strings and check the measurements. If they looked good I would sometimes drive the car around and check again or just call it done. I really depended on how much time I wanted to spend on it.