For those who have forgotten how or have never measured SWR.

Two separate voltage measurements are needed at two different places along
the line.
Slide the voltmeter along the line until a maximum is found.
Remember the reading, Vmax.
Slide the meter along the line again until a minimum is found.
Remember the reading, Vmin.
Before you forget, divide Vmax by Vmin.
You are left with a single number.
It has no dimensions.
It is the TRUE swr.

NOTE: In the above description and calculation there is no mention of Zo,
terminating impedance, source impedance, reflection coefficient, forward
power, reflected power, reflected volts, reflected current, Smith charts, or
conjugate matches. All these things are superflous to the determination. No
information other than the two voltage measurements is needed.

All other methods which purport to measure swr require injection of
additional information. And assumptions form an essential part of the
process. They can hardly be called swr measurements. Particularly when
they can indicate it on non-existent lines.