Roy, you are, at least, on the right track.

To measure SWR on the feedline, it is necessary to climb up the mast
or a ladder and insert an SWR meter, of the correcct impedance,
between the antenna and the feedline?

Then you have to come down safely to ground level, switch on the
transmitter, and view the meter reading through an astronomical
telescope, bearing in mind that the field of view with an astronomical
telescope is inverted with respect to normal.

In its usual position the SWR meter does not measure SWR on any line.
It merely indicates whether or not the transmitter is correctly loaded
with a resistive 50 ohms. Which is all anyone may wish to know.

After 50 years or more of ignorance, it is about time this hoax was
exposed to the world.

Then, all that is necessary to prevent the instrument from telling
lies, is to leave it where it is and change its name to TLI
(Transmitter Loading Indicator).
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Reg, G4FGQ.