There likely is a way to get it to work using the Quick Table Calculation method,
but I couldn't quite find it. However, I was wondering if it would suffice to write a new calculated field.
On your Percent Difference sheet, I tried a calculation with Visits and used a round-about formula of:
IF ATTR([Total].[Time Period Test])="Current Year" THEN
(2*SUM([Visits]) - TOTAL(SUM([Visits]))) / (TOTAL(SUM([Visits]))-SUM([Visits]))
This way the only Table Calculation is the Total which seemed to work
when setting a Compute Using of "Table Across". It did have the drawback
of having the empty Last Year column.
I didn't thoroughly check to see if it was producing all the right numbers,
or if it would work for all of your measures.
Please see workbook attached in the Forum thread.
269826diff_v10.4.twbx 249.9 KB