This code shows how to use Date Data in a calculation using the macro Report-Eval...

...pulled from ServiceRocket's site: http://community.servicerocket.com/servicerocket/topics/can_eval_data_be_used_for_date_data_calculations

Complete + 3 Weeks:

Date of Project Start

Date Project Completed

Today

Today - Start

(%global:current date > date:milliseconds% - %data:START > date:milliseconds%) / (1000 * 60 * 60 * 24) 
Complete - Start
(%data:END > date:milliseconds% - %data:START > date:milliseconds%) / (1000 * 60 * 60 * 24) 
Start Date:
(%data:START > date:milliseconds%) /(1000 * 60 * 60 * 24)
Complete Date:
(%data:END > date:milliseconds%) /(1000 * 60 * 60 * 24)