XpressDox give the template author the ability to perform calculations and other operations on the values of data elements, and to store those values in variables for later use in the template. One example of this is the ability to calculate totals on repeated data elements.
The contents of this article apply to Version 4 (and later) of XpressDox. Enhanced calculation support has been added in Version 9. If you have that version installed and are licensed for it, rather read