Abstract: This is a specialized hand-held and battery-powered unit for field testing of backflow valves. It displays and prints a permanent record of simultaneous source- and discharge-port pressure values and their difference. To reduce operator distraction and confusion during backflow tests the source and discharge values are automatically equalized, bringing the difference to zero, whenever the actually sensed pressures are within a threshold differential such as 0.2 pounds per square inch. Preferably two pressure sensors are provided for connection to source and discharge ports respectively, yielding independent analog electrical signals representing the pressures; and two independent analog-to-digital converters respond to the two sensor signals respectively. Digital input signals from the converters pass to a microprocessor--which controls a digital display to show the three values continuously.