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the star data in some parts of the sky.)  There is also a single-CD
subset of each dataset, known as SA1.0 and SA2.0.  Many of the
properties of the two versions are similar,  and they are commonly
referred to as "Ax.0" and "SAx.0".

   Getting a set of the Ax.0 CD-ROMs is not easy; the USNO didn't
make many, and reserves them for especially deserving applicants.
As of late 2001,  USNO was no longer producing or distributing the
CDs,  because they were working on a new version of the dataset.
However,  many people have the CDs,  and it is also possible to
download A2.0 data for a given part of the sky and to display that
data in Guide.

   To access Guide's Ax.0 functions,  click on the "Get A1.0/A2.0"
option in the Extras menu.  This will lead to a sub-menu of four
options.

   If you have a set of CDs,  or the SA1.0 or SA2.0 disks,  you can
zoom in on the part of the sky in which you are interested,  and then
click on "Get A1.0 from CD" or "Get A2.0 from CD".  Guide will figure
out which disk (or disks) are needed to cover that piece of the sky,
and will ask you to swap them in.  (If you've got an SAx.0 disk instead,
you can just ignore the "CD number thus-and-such" message and put in
the SAx.0 disk.  Guide will figure out that you're using that disk rather
than an Ax.0 disk.)

   After Guide extracts the data to the hard drive,  it will ask you to
put the Guide CD back into the CD-ROM drive.  Then it will refresh the
screen,  showing the Ax.0 (or SAx.0) stars.

   "A2.0 from Internet" works in a similar manner,  except instead of
asking you to insert a particular CD-ROM,  Guide goes out over the
Internet and downloads the A2.0 data from a server.  As with the "DSS
from Internet" option (discussed on page 56),  this is done in
the background,  so you can accomplish things while you're waiting for
the server to provide the data.  Once it's downloaded,  Guide will
refresh the screen and show the A2.0 stars.

   As with almost all objects shown on Guide's charts,  you can click
on Ax.0 or SAx.0 stars with the right mouste button to get information
and "more info" about them, and to control how they are displayed.

   If you have copied part or all of Ax.0 to your hard drive,  then
Guide can display it without going through these steps;  stars from
Ax.0 will simply be shown on the charts in the same manner as stars from
any other catalog.  To do this,  you need to edit the file GUIDE.DAT
with a text editor (such as Notepad) and add a line such as this:

A2_PATH=14.3;c:\a2

   The above line would tell Guide that if it's showing stars fainter

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