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on 28 Aug 1204 BC.  Since Guide is an astronomy program,  it sides
with the astronomers,  recognizes the year 0,  and expects -1203 to be
entered in the above instance.

   You can click on the days shown in the calendar for the current
month, plus the usual partial calendars for the previous and
following months, shown in the next six lines. This is a fast way to
back up or move ahead a few weeks.
                                                           
   The "Time Zone  UTC" option lets you tell Guide what time zone you
are using.  By default,  Guide displays all times in UTC (Coordinated
Universal Time,  basically Greenwich Time),  but clicking on this
option brings up a long list of the world's time zones.  You can also
select "time zones" such as Greenwich sidereal time,  local mean time,
Dynamical Time,  etc.  These are not really "time zones",  but
selecting them means that Guide will display all times in those
systems and will expect times you enter to be in those systems.

  The zone you select need not match the one used by your computer's
clock.  If you wish to have Guide show times in UTC,  even though
your PC clock is set to a local time zone, this is not a problem.
                                                              
  The "JD..." option lets you both see and reset the Julian Day.
The Julian Day system (no relation to the Julian calendar) is in
common use by astronomers;  it specifies time in terms of days
since noon, 1 Jan 4712 BC.  Thus,  1 Jan 2000 is JD 2451545.; that
is how many days will have elapsed since 1 Jan 4712 BC.  As you
alter the time,  the value shown here will change,  and if you
click on it, you will be asked to specify the time by Julian Day.      

   The "Time Format" option lets you choose how dates and times   
will be shown throughout Guide.  You can decide if dates should
be in YYYY/MM/DD form,  or MM/DD/YYYY form,  or perhaps Julian
Day form,  or given in decimal hours or decimal days instead of
the usual hours/minutes/seconds form.  You can also choose to have
dates shown in any of several calendars;  the most important of
these are the Julian and Gregorian calendars.  (The Julian calendar
is unrelated to the Julian Day system,  confusing though that is!)
                            
   The Gregorian calendar is the one currently used in most of
the world.  The Julian calendar was its predecessor,  and is almost
exactly similar.  Unfortunately,  its leap year rules resulted in
a "year" that didn't quite match the earth's actual motion around
the sun,  and by 1582,  a ten-day error had accumulated.

   So in 1582,  Pope Gregory declared that a new calendar would
be put into effect:  October 4 would be followed by October 15,
and certain leap days would be omitted in the future.  If you
look at October 1582 in the Time Box,  you should see this
odd state of affairs,  with ten days "missing".


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