The kadee wheel gauge has big slots for the flange edges, it does not do a good job of setting the back to back, not only are the slots too sloppy, they also measure the wrong place.
Trying to measure back to back using the knife edges of the flanges is wrong because it ignores the thickness of the flange. Thick flanges vs. thin flanges would give different back to back measurement. Also, different flanges have different contours at the very edge. so the Kadee gauge has a slot to handle more “blunt” edges, and thinner edges have a lot of slop.
It’s just a very poor way to measure back to back, and just as poor in trying to set gauge (actually worse since it cannot take into account the fillet).
It also only measures one measurement. The Aristo gauge had go/no go on a ton of different things, and it’s pretty darn close to the NMRA specs.
The back to back is correctly measured on the back side of the flange, where the “control surface” is when going through a switch.
The Aristo gauge is hard to find, but very handy and it was cheap. It’s worth the “hunt”
Greg