Running Sum

Hello all,

Hoping someone can help me out with this.

I've created a measure called 'Delta. Calculated as

DELTA = SUM(TABLE[WARRANTYUNITS]) - CALCULATE([AVG.WARR.]),ALL(TABLE))

AVG.WARR. is another measure calculated as

AVG.WARR = SUM(TABLE[WARRANTYUNITS]) / DISTINCTCOUNT(TABLE[MONTH))

I don't need a total sum of Delta, I need to add the result for Month 2 to Month 1, Month 3 to this and so on

The other picture is the table in excel using the correct calculation

I'm hoping to avoid linking the Delta by Month output into a new table so as to avoid refreshing the data continuously

Is there perhaps something I can do with time intelligence to make this calculate correctly?

Thank you for any help that may be provided!