In your sub summary layout part, you have to select a field as the "when sorted by" field--which is also known as the "break" field. You can use the summary fields with this break field in getSummary functions to compute a value consistant with the values shown in your summary fields when placed in the sub summary layout part:
GetSummary ( Total Hours worked ; Break Field ) / GetSummary ( Total Hours Available ; Break Field )
Just like your sub summary layout part, the results depend on your sort order and current found set of records.
Thanks - I appreciate the help.