So, if the scalar PD between A and D is the "true voltage" in the Lewin ring, then what @bsfeechannel showed above is a proper model for Dr. Lewins setup, right?

That means one can replace the induced EMF with a voltage source between A and D with the "true voltage" and that is then the energy source of the circuit?

But if this is really a proper model for Dr. Lewins circuit, it must also reproduce the meter readings from the experiment, right?

Only it doesn't. Hm. So, apparently it is not a proper model for Dr. Lewins circuit.

Maybe it's a proper model for the @jesuscf circuit? Apparently so, because he measured it with a few percent of error. He cannot say where this error comes from, but lets not go there now. But he also admits that if the probing wires were to follow a slightly different path, the error would increase.

So, @jesuscf found one single, very special path on which the \$V_{AD}\$ coincided with the computed scalar PD and yes, if in his circuit he replaced the induced EMF with a voltage source between A and D, the outcome would not change. But if he connected a second voltmeter between A and D on any other path, the whole model would collapse.