Train wheel rim measuring tool - GIF

[Inner]

What what aspect of the wheel are they measuring?

This was my question too so I did some searching. While I could not find the exact product, apparently it is better described as a wheel profile wear measurement tool used in routine maintenance to measure things like:

Flange height
Flange thickness
qR—value
Wheel rim width
Hollow run
Double skin

(I have no idea what qR, Hollow run, and Double skin measurements are.)

Also, it looks like all the cool kids now use non-contact laser systems to do this same thing.