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an object.

20b: Providing limits in RA and declination  

   By default,  Guide will assume that your dataset covers the entire
sky,  and will always examine it to see if any objects fall on the
screen.  But if the dataset covers only part of the sky,  and Guide
is aware of that fact,  it can sometimes avoid drawing the dataset
at all.  This can produce a substantial improvement in speed.

   For example,  if you look at RADIO.TDF,  you'll see that the 6C
Radio Sources II dataset has the following fields in it:

~ddeclimit 30  51   # This catalog extends from N 30 to N 51
~dralimit 8.5 17.5  # This catalog extends from 8h30m to 17h30m in RA

   It just so happens that this particular dataset covers a particular
"rectangle" in RA/dec.  Since Guide knows this,  it can (often) compare
that rectangle to the one on the screen, find that there is no overlap,
and deduce that there is no point in even considering this dataset any
further. If you have a lot of datasets each covering a small area (such
as the sections of the 6C radio survey), this can speed matters up
substantially.

   The "ralimit" field is unusual,  but the "declimit" one is not. For
example,  most datasets created in the Northern Hemisphere have a
southern declination limit (except for neutrino-based observations).

20c: Adding "More Info" and "click" data for your dataset   

   You will notice that each dataset also has a few lines starting with
a tilde (~~),  followed by "c", "r",  or "b". Each of these lines
involves showing some data when the object is clicked on,  when you get
remarks ("more info"), or both,  respectively.

   After the "~~(letter)",  two numbers are given:  the starting column
and length (as was true for most of the fields already discussed).
Guide first checks to make sure that this field is not blank.  If it is
indeed not blank,  Guide shows that field,  using the remainder of the
"~~" line to decide what the format should be.

   For example,  the following line (from the quasar dataset):

~~r 46   5 ^Color index^ (B-V): %s\n

   tells Guide that the quasar dataset stores color index data in
columns 46-50.  If Guide finds data in those columns (this is not a
"given",  since not all quasars have had their color indices measured),
then Guide will show "Color index (B-V):",  the color index,  and then
skip to a new line (that's what the '\n' means). Because this is a
"~~r" line,  Guide will only show this data in the Remarks, i.e.,  when

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