Ian White GM3SEK wrote:

And here you've made that big leap again. Where did "power" come from?
Nothing in what you or I have said above explains how come the meter can
read "Watts".

It is calibrated in watts assuming that:

Vfor^2/50 = Ifor^2*50 = Vfor*Ifor = forward power

Vref^2/50 = Iref^2*50 = Vref*Iref = reflected power.

This is in accordance with the laws of physics embodied in the wave
reflection model. '50' in the above equations is critical. In any other
environment besides 50 ohms, the assumptions are not valid and the
calibration will be in error.
--
73, Cecil http://www.qsl.net/w5dxp