Speedrange Propane / Butane Level Indicator
The Speedrange Indicator can be used on any Propane, Butane cylinder or a mixture of gasses. It has a magnetic backing which attaches to the outside of the cylinder and shows the level of the gas. Take a reading as you are using gas. When your cylinder is empty, simply remove the indicator and place on a new tank. It is safe, reusable (it is magnetic, so can be fixed to any gas bottle) & reasonably accurate.