how to compare to values in same field

[pavansonu99]

in the above picture u can see the first column  is year and 3rd column is sales i want difference of 1st 2 sales and next i want difference of next 2 sales for 2004 and for 2005 again i want differences of sales  for that year

can you please provide the expression.

thanks in advance

[rupamjyotidas]

Didn't understand the whole question:-). Probably this might work in script

Sales-Peek(Sales)

[Anonymous]

may be try this in pivot or straight table

SALES-RANGESUM(ABOVE(SUM({1}(SALES)),0,2)) 

[pavansonu99]

i want for year 2004 the differences of sales.

then i want it for next year like that