ISO 4064-1:2014|OIML R 49-1:2013 specifies metrological and technical requirements of water meters for cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the integrated volume. In addition to water meters based on mechanical principles, ISO 4064-1:2014|OIML R 49-1:2013 applies to devices based on electrical or electronic principles, and mechanical principles incorporating electronic devices, used to measure the volume of cold potable water and hot water. ISO 4064-1:2014|OIML R 49-1:2013 also applies to electronic ancillary devices. Ancillary devices are optional. However, it is possible for national or regional regulations to make some ancillary devices mandatory in relation to the utilization of water meters.