The gas meter shell is mainly made of aluminum alloy die-casting. The gas meter has the same principle as the old locomotive. It relies on the pressure of the gas to do work externally and push the roller counter to count. How to do it? The cylinder and piston mechanism in the locomotive have been greatly simplified, replacing the cylinder with a "wind box" and replacing the piston with a "thin film". The so-called "wind box" is nothing more than an empty box made of metal.