ABSTRACT
Accurate calibrations are needed for accurate measurements. Hydrometric current meters to study river hydrodynamics are often calibrated in tow tanks. An increase of sensitivity of current meters requires a thorough understanding of the water movements in the tow tank that might compromise calibration results. At the calibration facility for hydrometric current meters in Ittigen, Switzerland, current meters have been calibrated for more than 100 years. The uncertainty budget for the facility has evolved over time. In the recent years, a detailed investigation of the effects of waiting times between towing runs have led to the observation of surface gravity waves which cannot be neglected in the uncertainty budget of such a high precision facility. Observation techniques to measure surface waves will be presented as well as means to mitigate unwanted water movements in the tank.
