Get Average from Matric Column sub total for given years

[Sams11]

Hi All,
This is my table and displaying data by developer in row and Fiscal Year/Qtr in column showing total issue count & my need is to show only "total avarage" at the end of the table as grand average, can someone help with this calculation?

[wdx223_Daniel]

It is best to provide some sample data and simulate the results you want