ISO 4064-4:2014 applies to water meters used to meter the volume of cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the integrated volume. ISO 4064-4:2014 specifies technical characteristics and pressure loss requirements for meters for cold potable water and hot water. It applies to water meters which can withstand: a) a maximum admissible working pressure (MAP) equal to at least 1 MPa [0,6 MPa for meters for use with pipe nominal diameters (DNs) ≥500 mm]; b) a maximum admissible temperature (MAT) for cold potable water meters of 30 °C; c) a MAT for hot water meters up to 180 °C, depending on class. In addition to meters based on mechanical principles, ISO 4064-4:2014 also applies to water meters based on electrical or electronic principles, and to water meters based on mechanical principles incorporating electronic devices, used to meter the volume flow of hot water and cold potable water. It also applies to electronic ancillary devices. As a rule ancillary devices are optional. However, national or international regulations may make some ancillary devices mandatory in relation to the utilization of the water meter.