A diaphragm meter is a positive displacement instrument which is used to measure the volume of gas that passes through it. This is accomplished through the known volume that is displaced for each stroke of the diaphragm. The diaphragm also provides the seal between the measuring chambers of the device. As such the diaphragm meter has proven to be an accurate and reliable means of measurement of gas for many years. This is especially true at low flow rates because of its positive displacement characteristics. This paper includes a brief history of diaphragm meters, an explanation of the operation of the diaphragm meter, a basic review of the function and design of the positive displacement meter, discusses meter ratings and capacity, and introduces temperature compensation