I think Juranovich meant tolerance of holes being in the right location.

I’ve seen makers use the rails with hole transfer punches to make sure the holes are in the right place. Put the rail on the plate, loosely clamp down one end and then measure and tap to the right distance from the edge. Do the other end the same and then go back and forth until both end are perfectly aligned before clamping down hard... then one final measure to make sure the rail hasn’t moved.

Then if that is all correct, just go down the holes with the correct size hole punch and tap in the locations for the holes. Follow up with a drill press or a mag drill (you can even rent them according to my friend) and Bobbie’s your auntie.

This way, you won’t measure the hole spacing wrong and drop a hole out of position that would knock out the following holes too. Simples, as a certain Meercat would say.