Abstract: A method of measuring the speed of flow of a liquid along a conduit by omitting a continuous acoustic signal of known frequency through a wall of the conduit and receiving the signal reflected, from the liquid. This reflected signal is of increased frequency due to the Doppler effect, and the received signal is demodulated to give a signal at the Doppler difference frequency which is a function of the liquid speed. The Doppler difference frequency is divided by a divisor of known numerical value and the quotient frequency counted. This quotient frequency is a function of the speed of flow or the flow rate, and one or more indicator devices utilize this count either as analogue signal or integrated with respect to time to indicate the instantaneous speed or flow rate or the total volume or weight of liquid which has passed.