Thank you Larry, your suggestion doesn't work. Of course I set all the possible parameters before to write to this forum but nevetheless I checked again using your set.
If I set UCAC3 on Extra-User data I'm not able to see the GSC while showing UCAC3 stars.
At level 8 or above the GSC and Tycho stars desappear.
If I de-select UCAC3 I can see all catalogues I have installed (built-in, A2, UCAC2) at any level all together.
A question for Bill: I use the Italian version, can be the problem related to this?
Cheers, Stefano.

--- In guide-user@yahoogroups.com, Woodchuk <woodl@...> wrote:
>
>
> > I do have some ideas that might let that be possible eventually.
> > (Guide would show UCAC3 stars first; then, when drawing GSC stars,
> > it would ask: is this star within (say) 2" of a UCAC3 one? If so,
> > assume they're the same, and don't draw the GSC version. Then,
> > when drawing A2.0 stars: is it within (say) 2" of an already drawn
> > UCAC3 or GSC star? This would be pretty easy to do... had I planned
> > on such right from the beginning! The threshhold would have to be
> > user-adjustable.)
>
>
>
> The way I handle the USAC3 stars is to right click on a UCAC3 star and in the
> "Display" dialog box I set my FOV to 0°- 1.7° (as sort of a default), and set the
> "Limiting Magnitude" to about the same level as the "Limiting Mag" in the Star
> Dialog box.
>
> Then if I want a different setting (for example when printing a finder chart for
> Pluto) I will change both settings but when done I reset the FOV and mag limit back
> to the original settings. That way you always have a constant reference point.
>
> Others may select different settings, these work for me.
> I mainly use the TYC, UCAC3, A2, and selected GSC 2.3.2 stars.
> --
> Larry Wood
>