This Part of ISO 4064/OIML R 49 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. This Part of ISO 4064/OIML R 49 also applies to water meters based on electrical or electronic principles, and to water meters based on mechanical principles incorporating electronic devices, used to measure the volume flow of hot water and cold potable water. It also applies to electronic ancillary devices. Ancillary devices are optional. However, national or regional regulations may make some ancillary devices mandatory in relation to the utilization of the water meters. NOTE Any national regulations apply in the country of use.