It's common sense. Unless you want to load exactly at touch for some reason, it doesn't matter what any other length is referred to.That is highly debated.
If the accurate length is .010 (actual) into the lands, what does it matter if it is referred to as .005 or .015? The name you call it is irrelevant. Same with any measure off the lands, if your .020 off is actually .010 off, what does it matter? The precision comes in consistency you apply in adjusting from whatever length you started from.