[ferret_users] regridding 360_day to yearly data (yearly maximum)

[Peter Szabo <szabpet83@xxxxxxxxx>]

Dear Ferret Users,
I want time-series of yearly maximum precipitation on a day. To achieve this for every year i should have my data on a yearly grid in time. I have netcdf file for 30 years with calendar of 360_days. 

define axis/t="1-JAN-1961":"1-JAN-1990"/np=30/calendar=360_day yearly
let precip30=precip20[gt=yearly@max]

"precip20" is the original variable and "precip30" consists of 30 time. I wanted to supervise this with the below command:

fill precip20[l=1:360@max]-precip30[l=1]

I counted the maximum 1-day precipitation for the first year in different way. They should be the same, and this subtraction exactly zero. Unfortunately, it is not zero. 

Does someone know what mistake did i make?

Thanks, 
Peter Szabo