Matt Allington has a video for us:
The table on the left above shows the change in head count in each department, and is to be populated by the manager. But when it comes to reporting, we really need to know the total change in headcount as a number for each year, not just the first year the change occurred (as shown in the table to the right, above).
There are different ways to solve this problem, but I decided to do it using a combination of Power Query and DAX.
Click through for the video solution.