Intermediate SUM in a DP Macro

Hello,

I am not able to find the correct synthax for a macro with an intermediate calculation.

Here is the description of my issue:

1) My Macro run interactively.

2) according to the level display, I want the macro to calculate the Forecast Lag Deviation.(FLD)

Here is a example :

For one unique product displayed

FLD = (1 - (abs(Forecast Lag - Sales) )  / Sales ) * 100

For one family of product displayed, I want the same formula, but I want the difference (abs (Forecast Lag - Sales) to be the sum of each single product differrence

Example :      Forecast Lag     Sales

Family               200               300

Product 1             50               200

Product 2              150               100

If I run my current Macro, I have the following calculation KO:

FLD = (1 - (abs(200-300)/300))*100 = 66%

Here is the coorect calculation :

FLD = (1 - (150 + 50) / 300) = 33%

150 is the difference for product 1

50 is the difference for product 2

How can I convert this formula in a DP Macro ?

I imagine the solution with LAYOUTVAR which would be the intermediate sum of each product of the family, but I have no idea of the correct synthax.

Could you please  help me ?

Thanks a lot.

Pierre