Tom, W9JI wrote:
"It is only after the voltages, one proportional to current and one
proportional to voltage, are added that the voltage is rectified and
used to drive the meter."

Obviously a power determination must use voltage and current samples
taken at the same place at the same time. We can`t use today`s voltage
and yesterday`s current nor can we use the voltage over here and the
current over there.

Everything happens simultaneously and at the same sampling point.

A single loop terminated in a diode is coupled to the center conductor
of the coax. Its magnetic coupling produces the current sample. Its
capacitive coupling produces the voltage sample. These are tweaked for
identical deflection of the power meter.

Best regards, Richard Harrison, KB5WZI