Help needed, on Rangeavg [ How to exclude a Dimension when calculating RangeSum ]

[#1]

Hi, John Witherspoon I need your help urgently

Please help me to calculate the the Average Amount of next 3 coming row in a straight table chart but want to exclude some dimension when calculating RangeAvg, on every row like the table

I want to exclude the Dimension Design, SNo. in calculation of RangeAvg

Customer	Design	Machine	SNo.	Sales Amount	sum next  3 rows	Average
A	D-1	Mc-1	1	50	70	35
A	D-1	Mc-1	2	45	25	25
A	D-1	Mc-1	3	25	0	0
A	D-1	Mc-2	4	75	0	0
B	D-5	Mc-1	5	40	25	25
B	D-5	Mc-1	6	25	0	0
B	D-5	Mc-2	7	30	0	0
C	D-1	Mc-1	8	40	0	0
C	D-1	Mc-2	9	30	50	50
C	D-2	Mc-2	10	50	0	0
D	D-1	Mc-1	11	20	0	0

SNo. value of this column is comming from sql query [ Row_Number()  ], it is a running no

Last column is my desired result

I am attaching QVW sample here

thanks & regars

bb