Getting the Previous Value in a Matrix with 7 rows

You have interesting data including negative numbers. Calculating a WoW with a mix of positive and negative numbers is extremely subjective.  Make sure you agree with the formula.

Here's my (subjective) version:

Rev1 change = 
var pr1 = CALCULATE(sum(test[Rev1]),DATEADD('Calendar'[Date],-7,DAY))
return divide(sum(test[Rev1])-pr1,abs(pr1),1)

However your x axis is driven by a fact date (end of snapshot week) and not by the dimension date as it should be . You will want to correct that too ( or modify the above formula)