As you may know, the only way to determine how much CO2 is in your CO2 tank is by weighing it. CO2 is filled by weight. The Super Scale is an easy to use lightweight, digital portable scale that will quickly and easily tell you where your level of CO2 is. It is a good idea to weigh your empty cylinder before getting it filled and then check the weight of the full cylinder to insure that the shop did not under fill or over fill your cylinder (i.e. A full PT-10 should be 10 lbs. heavier than its empty weight.) We highly recommend this tool for RVers.