DSum for running daily total of hrs

From: jonefer (jonefer_at_discussions.microsoft.com)
Date: 10/29/04 

Date: Fri, 29 Oct 2004 16:25:03 -0700

Using fields:
JobDate
StartTime
EndTime
JobHrs
TotalHrsForThisDate

How can I use the DSUM formula to return TotalHrsForThisDate?

For Example:

Query should return the following:

JobDate StartTime EndTime JobHrs TotalHrsForThisDate
====== ====== ===== ==== =============
10/25/04 8:00 12:00 4 8
10/25/04 13:00 17:00 4 8
10/26/04 8:00 10:00 2 5
10/26/04 11:00 14:00 3 5