Hi folks,

It looks as if two very different things are being confused here.

After you use the A2_PATH= method in Guide.dat, _you do not
need to use the 'Extras... Get A1.0/A2.0 data... A2.0 from CD-ROM"
option_. The latter is intended _only_ for use with the CDs.

Instead, once the A2_PATH= method is set up, you can zoom
in on areas for which you have A2.0 data copied to the hard drive,
and the stars will pop up in the background. It's a much simpler
method; there's no need to extract chunks of A2.0 to your hard
drive. (As is only logical. After all, the A2.0 data now _is_ on
your hard drive.)

Elia, I think you did the right thing (your A2_PATH statement
looks reasonable). The one problem is this: you used

A2_PATH=20;x:\USNO\

Given this, Guide will only show the A2.0 stars if the limiting
magnitude is fainter than 20. That's pretty faint. Change it to,
say, 13 or 14, and A2.0 stars will begin to appear at that
limiting magnitude. (I use that level because GSC is passably
complete to that level.)

Joe, it's true that SA2.0 is _much_ smaller than A2.0. It fits
on a single CD-ROM (about 664 MBytes). But it's almost useless
for any purpose except astrometry. It contains about 10% of the
stars of A2.0, but these are not the brightest stars; instead,
they are 10% selected in an almost random manner, intended
to make sure that there are at least a few stars in any CCD frame.
All the stars selected are of intermediate magnitudes, because
these make the best reference stars for astrometry (bright enough
to give a good signal, but not so bright as to saturate a CCD chip.)

-- Bill