Most recent minus previous in pivot table total column
I have a pivot table that looks like this. I would like to add two totals column that calculates the difference between the most recent effort / attainment grade and the previous / attainment effort grade.
Business December effort = 4
Business September effort = 5
Total column (Most recent - previous) = -1
Ideally, if only certain dates were selected then the calculation would update to reflect the selected dates. E.g. if September and March 2018 were selected then most recent date used would be September (despite more recent dates existing in the data) and the previous date used would be March 2018.