gregk.......In theory, all four set of plates on the front should be the same and the the two sets on each rear should be the same. You can take the measurement at any of the four sets of plates up front and and either of the rear plates on each side.
Adjust the rears first to get the side to side accurate and then adjust the front. Air the coach down and then air up and check again.
I've always been amazed that all that steel is assembled on the front end with multiple joints, yet it all matches up when you measure them. Mine has always measured evenly and so did an 08 Dip that I adjusted. I did do an adjustment on a friend's Cayman R4R chassis and the front was off a 1/4" from side to side. It wasn't enough to be concerned and didn't cause any ride or wear issues.
Don & Mary
2019 Newmar Dutch Star 4018
2016 GMC Canyon 4WD Crew Cab