how to customize autofill in excel2010

Solution 1:

If you want your ratios in C2, C3, C4, ..., for example, enter

=(OFFSET($B$2,12*(ROW()-1),0) - OFFSET($B$2,12*(ROW()-2),0)) / OFFSET($B$2,12*(ROW()-2),0)

into C2 and autofill down to C3, C4, .... ROW() returns the row number of the cell it is in, so we get

row #     12*(ROW()-1)     12*(ROW()-2)
  2            12                0
  3            24               12
  4            36               24

OFFSET($B$2, number, 0) refers to the cell number rows below B2 (and 0 columns to the right).