K7ITM wrote in
ups.com:

....

Tom, for avoidance of doubt, I am not talking about the type of directional
coupler that uses a couple line and that you would terminate with matching
load. I am talking about the cheap VSWR meters that have about 100mm long
coupled line, that is quite tightly coupled, and the resistor at one end of
the line is adjusted to balance the electric field sample with the magnetic
field sample for a null reading with V/I=Zn.

Owen