Custom formula at row grand total in table matrix visualization

I have table grid which have 5-6 columns coming from 3 different tables have relationship. I want to apply custom formula on specific row grand total. 

The column contains data of week count for the specific machines.  Currently it simply applying sum() as grand total on the column data. I want to apply custom formula like (sum of week count)/(count of machines * 252). Count of machine I can get it from the measure. 

Thanks in advance.