Richard Harrison wrote:

Keith wrote:
"But the quantities being measured are line volts and line amps and
neither is proportional to incident or reflected watts."

Bird states:
"Where should the wattmeter be inserted? Again referring to the
formulas, we see that the elements extract a voltage proportional to
either Ef or Er, while the total E varies along an improperly terminated
50-ohm line, the component voltages do not. This is simply another way
of saying that the energy in the forward wave remains the same from the
source to the load, where some or all of it is reflected (unless the
load is 50 ohms) and that reflected energy remains constant from the
load back to the source.

It is not surprising that they should write this, after all they do
mark their instruments in watts, so they likely believe it.

But is it correct?

Our directional power meters can, therefore, be
placed anywhere between the source and the load."

This part is true.

I don`t guarantee a perfect copy of Bird`s Technical Series extract. You
should request your own copy from Bird.

Since the whole question is about whether what Bird does is correct,
they hardly stand as someone who can resolve the question.

....Keith