How can we counter check the LPG dispensing pump if it is really exactly correct volume of LPG dispensed?

Answer 1

Place an empty LPG tank on a scale and record it's weight.
Then pump the tank full, or with 25 to 40 pounds of LPG.
Record the final weight.
Then calculate the volume pumped based upon the weight of the LPG in the tank.

When I fill my propane tanks at our local propane fill station, that is how thy judge how much propane liquid I am buying.