On ours there are small adjustment screws on the monitor panel. They take a jewelers screwdriver. Just adjust them till the level reads what the actual contents are. Or at least that's the way ours work, and they will never be truly accurate.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA,
RV'ing since 1957, NRA Benefactor Life, towing '21 Jeep JLU Rubicon Ecodiesel