In backup software, delta files are used to store all the changes made to all the files you back up, so that it doesn't need to create -- and store -- a complete new set of files each day. You might wish to restore your accounting records as they existed, for example, yesterday, last week or last month, depending on when an error was introduced. The backup software will use the information in the delta files to reconstruct your records as they were on the date you choose.
What Is a Delta File? | eHow.com
Explanation of Name:
Science and mathematics have assigned meanings to various letters from the Greek alphabet for use in equations. Delta, the fourth letter of the Greek alphabet, is used to symbolize a change in value. Delta files, which record the changes between two computer files, get their name from this convention.
Now as for those numbers. Those could be values in the models/rez files, they could be locations, or a mixture of both.