More it is about a tuner's habit of showing a higher VSWR as the power
level is increased.

I have read that this is not the case. VSWR does not change with power
level, and that something is wrong with the VSWR meter, but what would
be wrong with the meter, and more importantly, *which* is correct, my
low power or high power, and how do I find out?

My Rig VSWR meter and my tuner meter read fairly close at the low end,
but diverge at the high end. But both read higher VSWR than at low
power. so that isn't a help.

I do have another VSWR meter, but at this point I suspect that adding
another variable will just further confuse me! 8^P

Anyone have an explanation?

Simple. This has been discussed many times. The diodes are nonlinear and
when on the low end of the voltage across them, they conduct differant.

To get the best indication of swr use the larger ammount of power. You can
use the lowest ammount of power to adjust the tuner for the lowest indicated
SWR . That will not matter. It is just the most accurate swr will be seen
by the meter at a higher power level.

If you use a directional wattmeter that has a wattage scale and calculate
the swr , it should be the same at all power levels provided the meter is
accurate.