This part of ISO 1100 specifies methods of determining the stage-discharge relation for a gauging station. A sufficient number of discharge measurements, complete with corresponding stage measurements, is required to define a stage-discharge relation to the accuracy required by this part of ISO 1100.Stable and unstable channels are considered, including brief descriptions of the effects on the stage-discharge relation of ice and hysteresis. Methods for determining discharge for twin-gauge stations, ultrasonic velocity stations, electromagnetic velocity stations, and other complex ratings are not described in detail. These types of rating are described in other International Standards and Technical Reports, namely ISO/TR 9123, ISO 6416 and ISO 9213, as shown in clause 2.