Meter for electricity (electric power and possibly accumulated energy).
Generic meter for a commodity.
GenericMeter, which defines a common structure but no metering registers by itself (they depend on the actual type of meter). All meters refer to metering a connection. If a physical meter delivers real-time information about the measured quantities (e.g. power), the meter driver is advised to put this information into the connection's respective sensor readings in addition to the meter's register's resource.