Can someone please provide guidance for this issue:

a snippet from the SGC website:
"One of the great misunderstandings in checking grounds is
that just because you measure continuity with a VOM, that you will have
a good RF ground. You MAY have a good RF ground, but a DC measurement
doesn't prove it. Remember, if you measure the resistance across an
inductor, it will show zero DC resistance to ground even though it's
impedance at HF frequencies may be quite high. Continuity is a good
check, but it does not certify your RF ground system."

I would like to understand how/what to definitively measure before and
after I make improvements to my mobile HF system (additional
bonding/grounding). What metric will provide clear indication that I
have indeed made an improvement. I do have an MFJ-259 available. I
have been exclusively looking at the SWR for indication but I am
starting to learn that lowering the SWR is not necessarily an
improvement. Is it to simply to measure the mobile vertical feedpoint
impedance before and after ?

73, dennis, k1drw