Combining proven stream gauging techniques with the latest in digital electronic technology, the Model 2100 was developed to make water velocity measuring faster and easier than ever before. Designed to read velocities in the range of 0.1 to 25 fps, the Model 2100 uses a two-inch propeller to rotate a fiber-optics bundle which gates a signal from a photodiode to a photo sensitive transistor. This signal is transferred via flexible electrical cable to the Model 2100 Indicator, where it is processed to display velocity directly in feet and meters per second with resolution to hundredths.