I always do the string method, I've been to the local Bill Julie twice and both times they made it so the steering wheel was off. They told me it was cause the rear was out or some other BS.
I set the string using a couple of chairs or whatever and find roughly the middle of the rack, then make sure that when I stick steering wheel on it is straight, otherwise I move the rack slightly till it is (no more than 1/2 a spline, got it!!).
Measure and adjust so the 2 strings are parallel to each other (in front of car width and behind car width) and equal from axle centres front & rear, either side. Make sure I don't trip over string then measure the wheel distance from string front/rear on each wheel. Reset strings after I trip over them cause I'm not watching and do again.
Then I compare the numbers from the measurements. I might have from string on front wheels RHF 110 RHR 112, LHF126 LHR128. This equates to 4mm toe in, not good, so I adjust track rods to get correct number. I do the same on rear and presto, straight steering wheel...
Sounds laborious, but by the time you set-up and do it you would otherwise still be waiting at the local bill julie for the guy to finish changing over the wheel clamps cause "your wheels are too small sir, this is going to take longer so we'll charge you the 4x4 rate".
My tires have been on 9 years and show no signs of incorrect toe, they also pick up more rubber on track than they wear off too.....
Daniel