A simple way to do a summation or product is using a FOR loop. For example, you could write the sum from I=M to N of a function F like this... SUM=0 FOR I=M TO N INC SUM,F(I) NEXT ...where F is a user-defined function that returns a numerical value. A product would look pretty similar... PROD=1 FOR I=M TO N PROD=PROD*F(I) NEXT