The front toe needs a datum point and that point comes from the rear, and it's called the thrust angle.
Most tyre shops if asked what are you aligning to would say each other... No you're not, the front wheels are aligned to the middle of the rear.
I am instructor in geometry and suspension calibration and i was asked by the biggest fast fit company in the UK to train their area managers.
Not knowing their level of understanding, i initially start at the basics. Nearly all of them didn't know about the thrust angle!. In the end i decided to drop the training because most cannot understand geometry for more than two hours.