HI, I have a file containing daily cumulative data. For exemple, if pi is daily precipitation: day 1: p1 day 2 : p1 + p2 day 3 : p1+ p2 +p3 ... day i : p1 + p2 + ... + pi-1 + pi ... day 365 : p1 + p2 + ... + p365 = yearly precipitation Now, I would like to calculate pi the daily precipitation, i.e. day 1 : p1 day 2 : p2 day 3 : p3 ... day i : pi ... day 365: p365 So, for each day, I have to substract the pi-1 value to the pi value. Is it possible to do that with Ferret ? Thanks in advance for any help