<P> In 1885 Ferranti offered a mercury motor meter with a register similar to gas meters; this had the advantage that the consumer could easily read the meter and verify consumption . The first accurate, recording electricity consumption meter was a DC meter by Dr Hermann Aron, who patented it in 1883 . Hugo Hirst of the British General Electric Company introduced it commercially into Great Britain from 1888 . Aron's meter recorded the total charge used over time, and showed it on a series of clock dials . </P> <P> The first specimen of the AC kilowatt - hour meter produced on the basis of Hungarian Ottó Bláthy's patent and named after him was presented by the Ganz Works at the Frankfurt Fair in the autumn of 1889, and the first induction kilowatt - hour meter was already marketed by the factory at the end of the same year . These were the first alternating - current watt - hour meters, known by the name of Bláthy - meters . The AC kilowatt hour meters used at present operate on the same principle as Bláthy's original invention . Also around 1889, Elihu Thomson of the American General Electric company developed a recording watt meter (watt - hour meter) based on an ironless commutator motor . This meter overcame the disadvantages of the electrochemical type and could operate on either alternating or direct current . </P> <P> In 1894 Oliver Shallenberger of the Westinghouse Electric Corporation applied the induction principle previously used only in AC ampere - hour meters to produce a watt - hour meter of the modern electromechanical form, using an induction disk whose rotational speed was made proportional to the power in the circuit . The Bláthy meter was similar to Shallenberger and Thomson meter in that they are two - phase motor meter . Although the induction meter would only work on alternating current, it eliminated the delicate and troublesome commutator of the Thomson design . Shallenberger fell ill and was unable to refine his initial large and heavy design, although he did also develop a polyphase version . </P> <P> The most common unit of measurement on the electricity meter is the kilowatt hour (kWh), which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules . Some electricity companies use the SI megajoule instead . </P>

Where are the induction type energy meters used