COMMODITY CONSUMPTION METER

摘要

A commodity consumption meter (2), of a type to which add-on circuitry (54) can be attached to provide at least one function ancillary to metering of the consumption of the commodity, comprises an electrical circuit (6) having metering means (20) for measuring consumption of the commodity in response to at least one electrical signal (vi and vv) applied to an input of said circuit and an interface circuit (22) for controlling data supplied to a display (8) which is connectable to the interface (22). The interface circuit (22) is operable in a first mode of operation to relay consumption data from the metering means (20) to the display (8) and in a second mode of operation to provide data to the display (8) from the add-on circuitry (54) connected to an additional connection (18) to the circuit.