Originally Posted by br1dge
Pressure drop was from the gas being cold. If you chill your tank before refilling, it will old more. With that said I have never had much luck with the high pressure side of the gauge being accurate anyway!
A proper fill will be by weight. It's easier to fill when it's cold, but you should be getting 5 pounds (if that's your tank size) either way. If they put more in there while the tank is cold, it could warm up on your drive home and blow the safety valve on the tank. A couple people have had that happen.
The high pressure gauge accurately tells you the pressure in the tank, but until all your liquid CO2 has boiled off, the pressure in the tank is unrelated to the amount of CO2 left. The only way to know is to weigh it.