Reg Edwards wrote:
A so-called directional wattmeter or SWR meter merely responds to the
magnitude of a reflection coefficient
[...]
Just a little box containing assumptions, preconceived notions,
suppositions, ambiguitiues and a lot of imagination.

The box responds only to the voltage and the current on the line. Those
are the only *physical* things it responds to. All the rest is about
ideas.

The basic design of the instrument is inspired by the idea of forward
and reflected V and I waves, and the idea of the reflection
coefficient. The circuit is designed so that the meter displays the
magnitude of the reflection coefficient on a linear scale.

The further *calibration* of the meter scale in terms of SWR and
forward/reflected power is then inspired(?) by yet more ideas - which
Reg so aptly describes as a mix of "assumptions, preconceived notions,
suppositions, ambiguities and a lot of imagination."


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek