Accumulative total
 

I have a weekly time sheet that has projects and time booked to these
projects. This is in the form of 0 to 1.0 per day (1.0 =10 hours) with
the sub total for each day adding up to 1.0. At the end of each week I
copy the current worksheet for the next week, deleting the daily hours
ready for the new times to be booked. I want a column that will give me
accumulative hours against each project. I been adding the weekly
total to the previous weekly total by using the formula
=SUM(J16+WE030606!K17). I have to keep altering WE030606 by seven days
each week or it just adds to the original. How can I update the
refernce to the previous week to get an accumulative total? Hope this
makes sense Thanks in anticipation.
Charles