Don't get caught without propane! The Accu-Level removable/reusable propane tank gauge fits all R.V. and BBQ propane tanks, and visually shows the exact level of gas remaining by the color of the strip! Turns from yellow to orange as you empty your tank. Easy to use, lasts for years, and will not fade in the sunlight. Proudly made in the USA!How It Works/ How To Use The removable Accu-Level propane tank gauge utilizes a very special yellow ink. When slightly heated, the ink will change color from yellow to orange. Upon cooling, it will change back to yellow. There is nothing that gets used up or wears out. This Propane Tank Gauge will last for years. When activated, this gauge automatically senses the propane in your tank and indicates the amout remaining. To activate this item and obtain a measurement, pour a cup of hot water down the propane tank gauge. Immediately the entire gauge will turn orange, however within a few seconds the lower portion will return to yellow. This returned yellow color level is the surface of your propane. To reactivate, pour additional water at the top. This gauge is fragile, and care should be taken not to tear or sharply bend the gauge. When not in use, it may be left on the propane tank.