Keith wrote:
"---does the reader believe the markings on the scale and think that it
is actually MEASURING the power in a forward and reverse wave?"

The wattmeter markings have been calibrated to indicate watts. One only
must measure a quantity proportional to watts then interpret that
accurately.

A speedometer indicates miles per hour but gets that from electricity
which is proportional to speed. Neither miles nor hours are measured.

Best regards, Richard Harrison, KB5WZI