[ferret_users] Monthly mean

[Arijeet Dutta <arijeet.uoh@xxxxxxxxx>]

Hi all
I have data in every 5 days interval, from 1993 to 2016, I want to
create monthly mean from it. I did the following

define axis/t=1:8766:1/t0="01-jan-1993:00:00"/unit=day tday ! from 5day to daily
let ufl = uf[gt=tday] ! interpolate (linearly by default)
let uflsm = uf[l=@spz:31] ! a filter with half-power point of about 37 days
define axis/t=15-jan-1993:15-dec-2016:1/t0="15-jan-1993"/ unit=month tmon
let ufmon=uflsm[gt=tmon] ! subsample to monthly

But when I am listing ufmon, I get values from l=4, no values from l=1 to l=3
Please let me know the mistake

Thanks & reg
Arijeet