Exclude a column from a filter

Anonymous In addition to your question, I saw how you used the data column inside the DATESINPERIOD function. This is not how you should do that. Either you have a dim dates you created or you use the autodate time table. 
For simplicity, let's say you use the autodate time, than your measure is:

DIVIDE(
	CALCULATE (
	    SUM ( 'Google analytics'[Number of sessions] )
	        * SUM ( 'Google analytics'[Average time per session] ),
	    DATESINPERIOD (
	        'Google analytics'[Date].[Date],
	        FIRSTDATE ( 'Google analytics'[Date] ),
	        -1,
	        MONTH
	    )
	),
	 SUM ( 'Google analytics'[Cumulative number of session each week] )
)

Pay attention to the version I used:
'Google analytics'[Date].[Date]

Also, you don't need the ALL argument as you play with filters on the date table anyway.

Showcase Report – Contoso By SpartaBI