Create Running Total of Inventory, then find when it goes negative

[DemingPDCA]

Looking to create a running total of Inventory and find when it first goes negative - but can't even get the running total to work!

Have a table that looks like this - and I'd like the Inventory over time to be a running total - but as you can see - thats not working:

Current Calculation: 

Inventory over Time = 
    VAR maxdate = MAX(_Calendar[Date])
    RETURN
    CALCULATE(
        SUM('Inventory Watch (Supply and Demand)'[Due Qty]),
        'Inventory Watch (Supply and Demand)'[CURDUE] <= maxdate,
        ALL('Inventory Watch (Supply and Demand)'[CURDUE])
    )

Not sure what I'm doing wrong - but its just giving me the line item qty. 

Here's my relationships - in case those are the issue:

[DemingPDCA · Accepted solution]

Got it to work (had to start over - but figured I'd share)

First Calculated the overall qty

Total Due Qty = Sum('Inventory Watch'[Due Qty])

Not entirely sure what I was doing wrong - but it seemed to start working when I pulled my Total Due Qty out into its own measure - but that may not have actualyl been correlated - I tried too many things at once!

Due Qty running total in Due Date = 

VAR PartNumber = SELECTEDVALUE('Inventory Watch'[Part Number])

VAR QOH = CALCULATE(Max('Part Master'[Quantity On Hand]), FILTER('Part Master', 'Part Master'[Part Number] = PartNumber))

RETURN

QOH + 

CALCULATE(

[Total Due Qty]

, FILTER(

ALLEXCEPT('Inventory Watch', 'Part Master'[Part Number])

        , 'Inventory Watch'[Due Date] <= MAX('Calendar'[Date])))