Precipitation 3/6 h

[Fil]

Hi everyone,

I'm trying to plot a precipitation meteogram from GFS 3h data but, for
example, +33h timestep has precipitation from +30h to +33h but +36h timestep
also has precipitation from +30h to +33h and +33h to +36h. So what I wanted
to know is how can I subtract precipitation like 30h = 30h - 27h, 36h = 36h
- 33h, 42h = 42h - 39h, etc, so that +30h/+36h/+42h/etc timestep doesn't
include precipitation from +27h/+33h/+39h/etc timestep.

Also how can I sum precipitation from +3h to 180h? I'm trying to draw the
total precipitation above the bars graph and I tried something like:

totalprec=sum(APCPsfc,t=2,t=180)
'draw string x y 'totalprec

But it doesn't work at all.

Hope someone can help me.

Cheers.