ABSTRACT Hydrological models (HMs) can be applied for different purposes. and a key step is model calibration using objective functions (OF) to quantify the agreement between observed and calculated discharges. Fully understanding the OF is important to properly take advantage of model calibration and interpret the results. This study evaluates 36 OF proposed in the literature. https://www.roneverhart.com/Wiley-X-CAG-1-Gloves/