week over week change 2 date dimensions

Hello,

Im lookin to monitor forecast changes on a per SKU level on a week to week basis. We create a forecast every week for 12 month period like this one:

My plan is to have something like this in a waterfall format so that we can see the changes against the previos week on a monthly basis, similar to how its shown bellow:

My plan is to use dax for this measure as seen in other post but due to it having two date tables(onr a calendar table , the othe a report reference date table), im having trouble creating it

anybody have any pointers on where shoid i start?

thanks