measure gauge and it will show you how much is left in your bottle. Always stay prepared with accurate measure . Measure your with this measure gauge, simply attach it to your for bottle cylinder with this magnetic. Safe & accurate reusable works on bottle. Magnetic backing allows for easy repositioning on exchange bottles. This product can safely and accurately measure the capacity, according to the temperature , measuring the temperature span of -10 C~120 C. Will indicate when levels run low, before depleting the supply! While using the BBQ, save money by utilizing more from each cylinder.