"Keith Dysart" wrote in message
...

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The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.
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...Keith

I don't think that the directional ammeter reads instantaneous Vt and It.
The circuits I am thinking of sample a length of line (NOT A POINT) so the
sample records average voltage (or current) from a period of time.

If I understand the methodology of the directional ammeter correctly, it
extracts energy from the wave from both magnetic (current) and voltage
components. If the components are in phase, they add, and that only occurs
with the wave going in the design direction. Yes, this is a reading of
power, not voltage or current individually. Current and voltage are
related by the Zo of the transmission line, so if we know current, we also
know voltage, and visa versa.

Agreed?

73, Roger, W7WKB