It's only a baseline check. Looking for large variances battery to battery in a series string or supposed parallel configuration.
Seyyore piano tuner should employ this test on his recommended balanced battery connection banks. I use 2.5 volts on my Rolls batteries.
My new project of the week is finding a truly affordable battery voltage reference device that BS proofs a DMM at or around 12 volts DC. Something that defines 12.00 volts + - .01 volts guaranteed. Call it an accuracy verifier. Too many crappy DMMs and gauges out there to suit me. Will share info. Good luck to me this is something I've never had to look for having a Tektronix scope. Maybe something like this does not exist in affordable form that a novice can employ.