Formulas within Formulas
When mapping variables within a formula, you can choose to map a variable to another formula. This allows you to set the values for that variable based on a separate calculation.
These sub-formulas can also have variables, which can also be mapped to formulas.
To map a variable to another formula, simply select Formula... in the attribute selection drop-down. A new Formula field will appear for the variable.
Once you finished setting nested formula up, you can collapse the dialog by clicking < Back to Variable List. To edit the nested formula later, simply select the variable from the Variables list.
Columns as Variables
Using formulas as variables, you can create very powerful, highly customized formulas - but managing all those sub-formulas can get tricky. An alternative approach is to build each sub-formula as a separate column, and add them to your formula using columns as variables.