Dsum With Multiple Criteria

Hi!
I have two related tables, one containing human resource information, the other containing a weekly record of hours worked by employees.

Here's the dilemma:
I need to keep a running total of hours available based on hours worked.

Employees begin each 7 day work week with 70 hours of time available. Any hours worked in that week are subtracted from the available hours for that employee. If there are two days in a row not worked during any given week, the 70 hours needs to automatically reset.

These hours are tracked in the Hours Available field (a calculated control which needs the Dsum expression) which should examine the Hours Worked field. Presently, the Hours Worked control gives a total of all hours worked for the employee shown on screen, but I need to examine the current work week to see whether or not an employee has worked more than 70 hours (it's a legal requirement.) If during any 7 day period counting backwards from the present date the employee had two consecutive days off, the employee becomes eligible to work 70 hours and the countdown starts again. In short, the total hours worked should be subtracted from 70 until 0 is achieved in any given week, unless the employee has had two days off (Hours Worked sum for two consecutive days =0.) I have attached a paired down version of the database for review.

Any ideas?

Tom