Reg Edwards wrote:

A so-called directional wattmeter or SWR meter merely responds to the
magnitude of a reflection coefficient usually, but not necessarily, relative
to 50 + j0 ohms. Half of the information, the angle, is discarded without
being aware of its existence.


Not exactly correct.

The phase information is not displayed explicitly
on a scaler instrument like the Bird meter, but
phase is definitely involved in the principles of
operation of the directional coupler.

Very seldom, if ever, do we care a feather or a
fig what the exact phase value is, but the
directional coupler is not balanced unless the
phase is zero.

All automatic antenna tuners utilize this fact.

Bill W0IYH