Abstract: A digital electronics system, such as a computer, includes circuits which provides signals proportional to the instantaneous voltage and current on the power bus to a microprocessor. The microprocessor uses these signals, the capacitance of the system filter capacitors, and the desired time for the system voltage to remain above a minimum voltage, to calculate an instantaneous voltage threshold. When the power bus voltage falls below this threshold voltage, the microprocessor provides a signal warning of impending power failure. The product of the voltage and current, i.e. the instantaneous system power, is displayed on an alphanumeric LED on the front panel of the computer.