you may wish to try this:
=GROWTH(sales,,{5},)
where "sales" is a insert-name-define (named range) that contains your data. In your case "sales" is the values for periods1...4. The {5} is an arry for the future period you want to project to. The formula above will tell you the sales you can expect in month 5 if you have the sales values for periods 1 to 4 loaded in range "sales." It can just as well predict the 16th period or periods {6,7}, that is periods 6 and 7 in the same cell. Remember to format the cell. JSW