A U-tube manometer for calibrating a differential pressure transducer or the like, wherein the height of working fluid in each column may be determined by the two-way travel time of an acoustic pulse launched from the top of each column against the top of the working fluid. The propagation velocity of each acoustic pulse is determined by a calibration target integral with each tube and located above the working fluid at a predetermined distance from each acoustic source. The generation and detection of each acoustic pulse is monitored by a remote processor and recorder which calculates the pressure differential between the two tubes of the manometer.