Abstract: A method and apparatus provide for the determination of the rate-of-rise of the level of a liquid, such as molten metal in a mold, in a reliable, accurate, and flexible manner. Molten metal passes from a container through an adjustable valve in an orifice to a mold. A microwave generator is connected to a microwave antenna located above the mold for transmitting microwaves to the surface of the molten metal in the mold. A mixer/detector is operatively connected to the antenna, and a computer is operatively connected to the mixer/detector. The computer processes the mixed signal received from the mixer/detector after it is converted to a digital signal. This digital signal is responsive to the Doppler signal caused by change in the level of the metal in the mold. The rate-of-rise of the surface of the molten metal is calculated in response to the digital signal, and is displayed on a monitor.