How can I add a calculated field to a pivot table that shows the difference between two series of data?

"There's no easy way of doing this AFAIK.

You could set Year as a column field, and then right-click on the data field > Field Settings and change it from a normal Sum to 'Difference from' / Year / (previous). This is a fairly awful solution, as you'll notice when you try it, but it's all I've found so far.

The only other way I know is to add a simple spreadsheet formula to the column to the right of the table. An equally poor solution but it does work and might be suitable for your needs."