Sleeper: DAX Formula sum previous period

[Cuscino]

Hi Everyone

I m lookng for a DAX Formula (Measure):

2018w1 2018w2
Demand 1 0
Stock 6 2
PO 3 1

Total 4 5

Total= Stock - Demand - PO
Basically the first period is normal, but those onwards should sum up also the previous Total

Demand, stock and PO are in the same table, Period in another one
I have a slicer with all the Components , and the first Period (in the example above) is always changing (the first one in the source table is 2015w1)

Thanks

[Bob Phillips]

Not sure I understand the data, can you post a sample workbook and tell us expected results?