John Popelish wrote:
To get the power in the reverse direction, the input and output are
effectively exchanged so that the forward power indication cancels and
the reverse power indication is produced by the sum of its voltage and
current d-c sample outputs.

Thank you for this concise summary.

Except it is actually an incorrect concise summary.

The directional coupler adds RF voltage from a sampling across the line
directly to a sampling of RF current past that point.

It is only after the voltages, one proportional to current and one
proportional to voltage, are added that the resulting voltage is
rectified and used to drive a meter.

The directional effect can be analyzed using wave theory or simple
circuit theory. The results are the same.

73 Tom