Several embodiments include a method of computing a phase composition ratio of a two-phase mixture in a pipe. For example, the phase composition ratio is a void fraction or a dryness fraction. The two-phase mixture can have one or more material substances that do not travel as a whole (e.g., at least two of solid phase, liquid phase, and gaseous phase or two liquid materials of different densities that do not mix). A load cell can measure, continuously, weight of the pipe and content of the pipe. Then, a computing system or a circuit can compute, continuously, a moving average of the continuously measured weight. The computing system or the circuit can compute a change in the phase composition ratio of the two-phase mixture based on the computed moving average.