GRUAN calls for an uncertainty for every measured parameter. This includes wind measurements as well. Differences in wind and position measurements by different GPS systems have already been noted and this topic is not trivial. Uncertainties as the best estimate for the level of confidence for a given measurement should be established from a detailed understanding of the measurement principle and a detailed understanding of the processing that leads to the final reported measurement. Limitations in the uncertainty estimate imposed by manufacturers should be minimized where possible and verified through independent redundant measurements. In the worst case scenario, uncertainties can only be estimated in the comparison of different systems.