To check the Propane level left in your cylinder check early in the morning and look for a line where the dew stops. Another way is to pour a cup of nearly boiling water down the side of the tank and see where condensation forms.
Another option is to weigh the tank. Weighing is one of the most accurate methods. My fifth wheel tanks are 30 lbs full plus the tank weight. So from there it’s easy to determine how much propane is left if I weigh the tank.