Hi Jacobo, and thanks for the nice words.
Since ultra-high vacuum is linear, yes, you can simulate gases independently and then just sum the resulting pressures at the end.
In practice, you need to use the correct tools to make post-processing easier.
Most probably you'd first like to set up a transparent, rectangular facet that runs along your vacuum volume, and add a profile to it that will sample your pressure in that direction.
Since your simulation is time-dependent, you'd then use the Timewise Plotter to show the pressure during several moments. In fact on the bottom left, you can write a list of moments that you want to display. In this example 1,1,32 is a list of moments 1, 2, 3, ..., 32. You can use the semicolon to write inidvidual moments.
You can extract data from the Timewise plotter (right click then Copy to Clipboard) then paste it in an Excel sheet where you'd sum the gases manually.
A few hints for using moments, though: if, for example, you define 1000 moments, all textures, profiles, etc. will be stored 1000 times, so watch for your filesize and RAM usage.
Also, if you're only interested in the time-dependent results, then probably you want to disable "calculate constant flow" in the moments editor.
Get back to me if you need help with a conrete step, the documentation of the time-dependent mode isn't complete...
Cheers, Marton