Finding the "true zero" is utterly irrelevant to finding the right grind setting for your espresso machine. However, it only takes a second. Just depress the locking mechanism and rotate the hopper to get the burrs as close together as you can. That way you know at which number your burrs touch ... which is information that I never really found particularly interesting or important.
What is important is having plenty of coffee on hand so that you can dial the grinder in properly.