Date slicer, need the difference of value

Hi,

I have a field with values in them, let's say it's called sales.  And I have a master calendar table linked via Date field.  What I'm trying to show in a table or chart is, what's the difference in value by the two dates selected with the slicer.  Just say I picked 01/06/2018 to 31/06/2016 and the value on the 1st of July was 10 and on the 31st July it was 20, I want my result to show +10, as that's the variance from starting and ending points.

Thanks in advance.