date calculation - newbie needs help

I have two date/time fields and I want to display the "response time", in hours, between the two. Each field is in a seperate
table and is formatted as a long date which includes the time ie 31/12/03 14:45

The calculation must be based on a working day of 08.30am to 5.30pm, Monday to Friday so that 4:15pm on friday and 10:00am monday gives a result of 2.75 hours.

I've tried playing around with the workday function and datepart etc, but cannot get anything to work.

Does anyone have any ideas?

Look at the attached Sample DB

It assumes that there will never be more then a one day lapse of time between the weekdays or 3 days over weekend. You will have to modify it for different conditions, but this should get you going in the right direction

S-

S, you're an absolute star. I've been hunting all over the net for a solution and yours is the simplest, most elegant solution I've seen. Many thanks for your assistance.
Tintin