Hi Ming, Take a look at this FAQ, which shows some examples of of computing annual averages, and see if it gives you an idea of what to do. Write back if you need more help! How can I produce a time series of annual averages (or other intervals) from a monthly time series? http://www.ferret.noaa.gov/Ferret/FAQ/analysis/annual_from_monthly.html Ansley Ming Yang wrote: Hi, guys I have a 400 year long NC file and each record is monthly averaged, so that totally I have 4800 points in time axis. Now I want to calculate the average value for each year, how can I do that in Ferret? Ming |