With the greatest respect for Lawrence, I find in favor of declaring Poynt99 the winner of this debate.
While it may be possible to use a math setting on the scopes to multiply the RMS values of voltage and current this would only work for purely resistive loads where no phase angle exists. In order to accurately calculate the Average Power using the RMS method the phase angle must be included in the calculation.
Using the MEAN of the instantaneous power automatically handles the phase angle problem by removing the reactive power from the total, thereby leaving the Average Power, or Real Power.
Good Job Guys!
