This invention relates to a system for simulating a power plant synchroscope in which a digital computer supplies the information which indicates when two alternators are, or are not, in synchronism. Digital words are supplied by the computer to two separate registers whose parallel outputs are applied to the inputs of two separate frequency multipliers, one for each register. A single oscillator supplies its output to the second inputs of both of the multiplier, and the frequency of the oscillator is therein multiplied by the value of the words from the computer. The outputs from the two multipliers are supplied to two separate channels, one representing each of the two alternators. The square waves in each channel are converted into sine waves which are then applied to the incoming and running windings of a standard synchroscope. In addition, the information in the two channels is applied to the inputs of a phase difference detector which produces a digital phase difference.