Abstract: A rainfall rate gauge contains a turbine which turns on a horizontal axis and floats in a chamber about half full of water. Turbine motion is measured and electronically recorded by an optical sensor. The blades of the turbine have a reverse rake so that the a portion of the water captured in each bucket is carried above the water surface before being released when the blade tip breaks the water surface. This arrangement prevents unrestrained free wheeling of the turbine, and results in more precise measurement, particularly at very low rainfall rates.