How do you know how much gas is left in your cylinder? Weighing the cylinder is the only accurate way to tell the residual contents. However if you warm the cylinder with a hot cloth at about the level you think the gas is at, you will find that the metal will cool quickly at the level of the gas and stay warm above the gas level. If you choose to use a dish cloth, it would be a great idea if you also dribble a little water on the connections and do a leak check at the same time. Bubbles will form as the soapy water runs around the connections.