backwards YTD formula

[Costa]

Hey there,

i have data which in the measure always shows the YTD value.

Position	Month	Value (YTD)2
Apple	1	10
Apple	2	15
Apple	3	25
Apple	4	30
Apple	5	40
Apple	6	50
...	....	...
....	....	....

can I somehow use the set-analysis formula to calculate the monthly values?

January = 10

Febuary = 5

March = 10

April = 5

....

I don't want to calculate and create and data sets by scripting.

Thanks for your help 🙂