Line power measurements are commonly required to evaluate the performance of devices or circuits. Modular digitizers can make these power measurements. Digitizers are voltage responding measurement instruments. They can also measure current using suitable current probes or current shunts. Acquiring current and voltage next leads to calculating power based on the product of the acquired current and voltage waveforms. Power is the rate of transferring energy in a circuit and it is described by a number of attributes such as real, apparent, reactive, and instantaneous power. This application note will address making basic power measurements in AC circuits and devices using a modular digitizer.