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George Huxtable pointed out that the routine I posted
for converting a sexagesimal angle to decimal degrees
does not properly handle negative angles.  It wasn't
intended to.  It was intended as a simple solution
to a simple problem.  There is an obvious tradeoff
between completeness and clarity.

If you wish to accommodate signs, a simple solution is
to add another column, coding it as -1 or +1.  If the
data to be entered is Lat/Lon or Declination, then one
could code it as "N", "S", "E", or "W" and compute the
sign from that.  Then, for safety, one could take the
absolute value of DD, MM, and SS.

I intended to add that for spreadsheets it is usually
convenient to add a "Radians" column, where the angle
in degrees is multiplied by pi()/180.  This is because
trig functions in Excel and other spreadsheets expect
angles to be in radians (a "feature" that I find
annoying).

When I code this sort of thing on an HP-48 series
calculator, I find it convenient to enter numbers in
degrees, minutes, and tenths as DDD.mmt, that is, 32
degrees 15.2 minutes is entered as "32.152".  The
program then converts this to degrees and decimal
fractions of a degree internally.  My routines are
coded such that positive number inputs are interpreted
as N or W and negative number inputs as S or E.  The
calculator has built-in routines for doing the same
sort of thing for time in hours, minutes, and seconds.
 For example, 08:53:55 is entered as 8.5355 and
converted internally.

When I code on a TI-83+, I find it convenient to code
the program so that one enters degrees in one step,
minutes & tenths in another step, then N/S/E/W in a
third step.  The messy details get hidden inside the
program.

Best regards,

Chuck Taylor
 48d 55' N
122d 11' W




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