Headlight Alignment

As long as we are discussing ingenious ways of doing alignments, what is the
best way of aligning the headlights? Yes, I know where the screws are and
even how to operate a screwdriver; my issue is how do you know when they are
correct? Other than when people stop flashing their brights at you, of
course.
David Lieb
1972 RWA Midget