Checking subs ohm multimeter

[mdwerner6942]

I was checking my son's sub both dual 4 ohm when my Sundown SA-15 showed up, dual 2 ohm sub, but little confused this is new for me, we tested voice coils and get 3.2 ohms on each 2 ohm vc, someone mentioned touching the ends of my multimeter together and subtract it from 3.2 which confused me as on 4 ohms they just tested out just under 4 ohms, is there a difference on a 2 ohm test this way that I am missing? Yes you get around .7-.8 if you touch the DDM ends together, just wondered why a 2 ohm would not show up under 2 ohms on meter, I guess is the best way to ask it or explain it. Why a 4 ohm we got the right reading from the meter and not the same with the 2 ohm. Just trying to understand did it to make sure vc were good, then noticed 2 ohm test was off or seemed off maybe because I do not understand something. not sure please advice if you know.