CDO

Hello,
This is joana from IDL in Portugal.
In our institute we are wanting to use cdo to interpolate eta_levels to model_levels.Basicly we want to interpolate the sum of vars PH and PHB (named PHPHB) to lets say the velocity levels.
We want to do a simple vertical averaging from 27 vertical levels to 26 vertical levels, like in the example attached.

where PHPB has dimensions(time,level,xlat,xlong).
I've encountered the operator intlevel and intlevel3d, but the description lacks of practical examples, and i am not sure if this is the right path to follow.
We have some urgency in this matter, because is for some example vars for students to manipulate.

many thanks in advance
cheers

Joana de Medeiros
IDL/FCUL
Lisbo, Portugal