A very convenient way to adjust antenna tuners is to use a handheld
impedance analyzer as the signal source. I happen to use an
AEA CIA-HF, which can graph the SWR across the band. Not only can I see how
broad or narrow-banded the tuner's "solution" is, but I
can also easily see which way things change when I turn the various controls of
C and L. I tweak for the solution that gives the
broadest, flattest match.
Lastly, the signal level emitted by the analyzer is very low so QRM on the
bands is reduced.
-- Eric K3NA