Hi, Recently I started working with netcdf IPCC climate model data and I am using R to analyze these data. Some problems occur while doing this, as I am using the output of different climate models which are different in for example time calendar and grid coordinates. To analyze monthly means I have been using the function /chron/ for 365 day calendar time series. Originally the time is in numbers (1,2....,14600). This is for the timeperiod: 1961-2000. library(chron) syntime <- var.get.nc(nc, "time") time =chron(syntime, origin=c(month=1, day=1, year=1961)) jan <- months(time)=="Jan" feb <- months(time)=="Feb" mar <- months(time)=="Mar" apr <- months(time)=="Apr" may <- months(time)=="May" jun <- months(time)=="Jun" jul <- months(time)=="Jul" aug <- months(time)=="Aug" sep <- months(time)=="Sep" oct <- months(time)=="Oct" nov <- months(time)=="Nov" dec <- months(time)=="Dec Now I can use for example mean(pr[jan]) to get the monthly average of precipitation (pr) for January. However, I cannot find how I can change the 365 day in a 360 day calendar for the 360-day data that I have (the 360-day calendar has 10799 days for the same 1961-2000 period). Is there anyone who can help me with this problem? Thank you in advance. Kind regards, Saskia van Pelt