Evaluation of significance of slope changes in double‐mass curves

The double‐mass method is commonly used in the interpretation of precipitation records. Interpretation of double‐mass curves frequently involves rejection or acceptance of indicated changes in slope. Often, the decision must be based on inadequate station records. In any case, it is important that the analyst should know the probability of getting an abrupt slope change purely by chance. The significance of any slope change can be evaluated by a statistical treatment making use of range instead of standard deviations. The application is simplified by a special protractor and simple nomograph.