CIE4440. Introduction: Relation of purpose of data to data requirements. Relation of data to costs. Accuracy requirements of measurements and error propagation: Related to a problem the required accuracy of measurements and the consequences for accuracy in the final result are discussed. Different types of errors are handled. Propagation of errors; for dependent and independent measurements, from mathematical relations and regression is demonstrated. Recapitulated is the theory of regression and correlation. Interpretation of measurements, data completion: By standard statistical methods screening of measured data is performed; double mass analysis, residual mass, simple rainfall-runoff modelling. Detection of trends; split record tests, Spearman rank tests. Methods to fill data gaps and do filtering on data series for noise reduction. Methods of hydrological measurements and measuring equipment: To determine quantitatively the most important elements in the hydrological cycle an overview is presented of most common hydrological measurements, measuring equipment and indirect determination methods i.e. for precipitation, evaporation, transpiration, river discharge and groundwater tables. Use, purpose and measurement techniques for tracers in hydrology is discussed. Advantages and disadvantages and specific condition/application of methods are discussed. Equipment is demonstrated and discussed. Areal distributed observation: Areal interpolation techniques of point observations: inverse distance, Thiessen, contouring, Kriging. Comparison of interpolation techniques and estimation of errors. Correlation analysis of areal distributed observation of rainfall. Design of measuring networks: Based on correlation characteristics from point measurements (e.g. rainfall stations) and accuracy requirements the design of a network of stations is demonstrated.