As an added convenience, Impact already has some commonly used variables and expressions written and saved in the database. These variables can be accessed by choosing Add Library Variables.
To use this feature simply select the Add Library Variables function. You will be presented with an Add from Library window where you can choose from the Common Variable groups created in the Master Tool Settings. These groups would typically include Corrugated, Display and Folding Carton. Select the desired variable and click the Add Variables button to incorporate it into the Variables Window. The variable(s) can now be applied to dimensions using Assign or added to any expression.
Variable selected from Library
Variable added to Project/Layer
NOTE: You can select the folder and click Add Variables to add all of the variables that it contains instantly or select multiple by clicking while holding either the Shift Key or the Ctrl key.