hi meridian
this is an instrument that we can test , in fact compare , windings.
it applies an impulse to a refrence winding and save the wave form of trasiant vibration of it then other windings could be tested by apply the same impulse and comparision of their treansiant vibration with the refrense wave form
Sounds like a TDR with template matching. A short pulse is introduced to the coil and then the echo trace is recorded. A template is made from this and other coils responses are compared to it. Have a look at