The Variables Tab in the Impact Explorer provides for many Parametric variable functions. These functions include but are not limited to, creation of variables, grouping of variables, editing formulae and assigning variables to the dimensions.
The tools accessible under this tab allow for manual adjustment of variables and expressions while providing for quick testing to verify how the design will resize.
To access this tab simply click on it in the Impact Explorer.
The tab gives access to Project Variables and Layer Variables. General information is given in the Variables Window description.