Subtract previous date with current day in current sprint

i’m trying to create a projection line, for this i need to subtract total planned - start value in the first day and in the second day first day - productive needed

the logic are this

total hours = 71,25
productivity = 71,25 / workingdays(10) = 7,125

and i need to calculate the projectio thath is

day 0 → 71,25
day 1-> 71,25 - 7,125(productivity ) = 64,125
day 2-> 64,125 - 7,125(productivity ) = 57
day 3-> 57 - 7,125(productivity ) = 49,875

and so on

my doubpt is how could i get this measure ? i already have the values as the print bellow, but how can i create the measure to subtract betwen the days ?

Excel logic

i tried to use

but no sucess


Please, check the following formula for the projection calculation:

[Measures].[start value]
--daily expected burndown
([Measures].[start value]
[Measures].[Sprint length])
-- days since Sprint start
DateDiffDays(DateWithoutTime([Measures].[Sprint start date]),

Sprint length is another custom measure:

  [Measures].[Sprint start date],
  [Measures].[Sprint end date]

Janis, eazyBI support