In addition to the series of turbine gas meters, Elster-Instromet started to develop rotary gas meters over twenty years ago. The greatest challenge was to develop a reliable unit which should be independent of all installation effects. The unique measuring cartridge was developed to meet this objective. The unit basically consists of the measuring module and the pressure casing, which separates the flow rate measurement from the rest of the process. The result is a reliable high-performance unit that offers exemplary flexibility.