Abstract: A flowmeter for fluids comprising a transparent vertical tube widening in upward direction, a ball freely disposed within said tube so as to be carried upward in dependence upon the flow, and a plurality of helical guide members on the inside of said tube, the guide members having inner edges which extend substantially vertically so that the free cross-sectional area for movement of the ball is substantially the same at all heights of the tube, the guide members minimizing pendulating of the ball and thereby increasing the accuracy of measurement.