Hi Owen,
If you've got the A2_PATH variable set, then you shouldn't need that
tool button at all.
With the A2_PATH variable set, Guide will simply grab A2.0 data as you
zoom around the chart. The toolbar button was very much needed back when
we all had smaller hard drives; it relieved you of the need to copy the
entire A2.0 to your hard drive. Instead, you'd zoom in on your area of
interest, select that function (it was in the menus back then), and
Guide would prompt you to insert one of the eleven A2.0 CDs.
It would extract the data and then prompt you to put the Guide disk
back in. With any luck, this is all ancient history now; most people
will just copy the eleven CDs (all 6.3 GBytes of data) to their hard drives
and use the A2_PATH function.
Which still leaves the question of why A2.0 isn't showing up... and I
see Denis beat me to it. I just read my own documentation at
http://www.projectpluto.com/update7.htm#ax0_direct
and see that one has to specify the limiting magnitude at which A2.0
kicks in. You might set, say,
A2_PATH=14.3;c:\usnaoa2
The idea behind this is to avoid a case where you zoom out to a 180
degree field of view, leaving Guide sifting through all 6.3 GBytes of A2.0.
Instead, A2.0 is only shown if the limiting magnitude is fainter than
(in the above case) mag 14.3.
-- Bill