What kind of accuracy

The accuracy is printed on every level both for the vial up, and vial down readings. This means that they have a guaranteed maximum inaccuracy of .029 degrees, which means plus or minus 1/32“ (in) over 72“ (in). You could get a level that is plus or minus zero (0), dead accurate, but you will never get a level with a runout greater than plus or minus 1/32“ over 72“.