how accurate are the sensors and propane sensor for levels

One problem with those "Empty,1/3,2/3,Full" sensor systems is that you don't know if the level is actually 2/3, or is it just barely below the full sensor. Is it really "Empty" or is it just a tick below the 1/3 sensor. There are more accurate sensor systems that read out in percentages using external sensors that don't gum up, but few RV manufacturers install them since they cost a few dollars more.