Converting 6-hour Data to Daily Averages

[Jeremy S Pal <jpal@xxxxxxx>]

  Hi -

I am trying to compute the daily average of some 6-hourly data.  Does
anyone know of a way to do this using ferret?

Also, is it possible to use variables in the arguments defining the plot
range?  Here are two examples (that do not work) that better describe what
I want to do:
   yes? let t1=1
   yes? let t2=4
   yes? fill preca[l='t1':'t2']
 - or -
   yes? repeat/l=1:20:4 (let t1=l; let t2=l+4; plot/vs/over preca[l='t1':'t2'@ave], swi[l='t1':'t2'@ave])


  Thank you,

  - Jeremy