Owen wrote:
"---I can understand Reg`s point that the direct way to measure VSWR
requires sampling voltage or current over a quarter wave of line where
you can find / observe the actual minimum and maximum."

Yes, and the direct way to measure MPH would be to measure the number of
miles and divide by the number of hours to get an average value. It`s
not often done that way. Maybe about as often as people find maxima and
minima on a transmission line and compute their ratio.

It is more convenient and sufficiently accurate to use indirect methods
for MPH and SWR.

Best regards, Richard Harrison, KB5WZI