Adding usages manually allows you use a function to almost any parameter in the model that doesn't specifically allow for it in the main user interface. For example .
To open the Metaparameter Explorer, right click on the required function and choose Add Usage.
Suppose you want to calibrate the storage routing exponent (m) on one of the reaches in a Source model. Initially, identify which link or node in the model you want to place the expression in. Then add the function usage manually to allocate a parameter to the variable (steps outlined in Figure 1).
Figure 1. Adding Function Usages Manually
