Maybe someone can give me a reference to how I can define a new Category in
the Format Cell dialogue Number tab and how to create equation functions.

What I want to do is develop an add-in to Microsoft Office Excel 2003 using
C# or VB.NET. In the add-in I need to do two items:

1) I need to define formatting categories. An example would be to format a
floating point number into either a latitude (dd:mm:ss.sssss [N|S}) or a
longitude (ddd:mm:ss.sssss [E|W]).

2) The other item I need to accomplish is to add functions to the list of
available functions. For example to compute the azimuth from station1
defined by latitude, longitude, and elevation, to another station.

Regards,

JimM