Matt is right, but let me suggest an alternate method that should be easier and perhaps even more accurate.
The tires have a mold mark that runs around the center of the tire. The mold mark is going to be uniform on all tires and gives a place to measure from. The trouble is finding a place to measure from. Pick a spot on a tire other side of the vehicle and also has a clear line at a point as near as possible to 180° to the first spot. If you could measure at the 6:00 position to the other wheel, then you would aslo want to measure as near as possible to the
12:00 position. Obviously, the 12:00 position is going to present issues, so you have to go towards 11:00 or 1:00, deviate at the bottom of the tire the appropriate amount to measure two points 180° apart.Odds are that the axles are bent on a verticle line, making the desired measuring points to be the top and bottom of the tire. I don't have a clue as to how far it is from the mold mark on one tire to the mold mark on the other tire, but whatever your measurement is, you want the same measurement when you shift 180°. If it is 48 and 7/32nds at 12:00, then it should be 48 and 7/32nds at 6:00. I suggest the variance should be less than 3/64ths, which is 1.5 32nds. 4 32nds is 1/8th. So, the deviation is well under an
8th. Measuring from the rim will give the same result, but measuring to the rim is difficult and the added difficulty can affect an accurate measurement. The mold marks on the tires give a flat place to measure that is unobstructed at the point where the tape is held and read. Your partner needs to understand that the tolerance is very small and the error probability is very high, so the tape must be held at the same point. Instead of measuring from the end of the tape, I sugggest using the 1" or 2" mark as the starting point because the lines are smaller and getting the starting point at the same place for all measurements is critical here.Having said all of that, the alignment shop should be able to set a fixture that will give an accurate measurement for you. They won't be able to adjust very much, but they will be able to tell you if the axles are bent.