A record of every change made to a WEAP area is logged in the text file "Changes.txt," which is stored in the subdirectory for a WEAP area. Each change is tagged with the date and time of the change, as well as who made it. You can also get a customizable report inside WEAP of all changes made to expressions -- go to the Data View and select this History tab.
The History tab can save the listed changes as a Visual Basic script (Save As Visual Basic Script) that makes the same changes when it is run in another copy of the area, so that changes made by several people in separate copies can be merged. The script records who made each change. When it is run, WEAP asks whether to merge the changes, and the option "Attribute changes to original user" logs each change under the person who originally made it (whose user details are added to the area's user list) rather than the person running the script. Area > Change History by User summarizes who has worked on the area and when, with the scenarios they added and the versions they saved.