The fact that a given SWR meter says its load is matched does NOT prove
that its input is matched. The only way to compare your two meters
(internal and external) is to tune the tuner for a match on one, remove
it from the circuit and see if the second (e.g. internal) meter agrees
with the match.
It's easily the case that the two meters don't read alike. But its also
likely that the impedance seen through a SWR meter is not precisely that
which it shows as 1:1 SWR on its load connection. It can introduce a
detectable change in SWR. I know Bird's do that, I expect others do it
too.
73, Jerry, K0CQ
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