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To display power, a meter measures various voltages and currents in a circuit. For two-wire, single phase AC, voltage is measured line-line (or line-neutral), either directly or using a potential transformer. Line current is measured directly or through a current transformer, as shown in the diagram. The combination of one voltage measurement and one current measurement means this meter has one element. A 3-wire, single phase AC circuit requires two voltage measurements (L1-N & L2-N) and two current measurements. This is a two element meter.

Measuring power in a 3-wire, three phase delta circuit requires two phase to phase voltage measurements (e.g. L1-L2 and L3-L1) plus two line currents. This is also a two element configuration. A 4-wire, three phase WYE circuit can be measured with a three element meter. It reads each line voltage with respect to neutral and each line current. Some meters can also calculate power in this circuit with only two voltage readings. This is a 2½ element configuration.

In addition to the proper voltage and current levels, a power meter must have right number of elements for the system configuration to be monitored.