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Hi Brad,

When I wrote that the blue overlay (actually my 1958 U.S.Navy 2102-D
instructions call it a "blue template") doesn't seem to work correctly
in S hemi latitudes, it was because I didn't expect that the blue
template would continue to keep a "north perspective" after the zenith
crossed the equator into the southern latitudes (on a real 2101, the
zenith doesn't cross over to the outside of the equator). But I
realize now that mathmatically it is correct. Actually, the more I use
it, the more I like the way it works, and I no longer think it should
be changed so that the overlay should switch to a South perspective
automatically. After all, when using a real 2102-D, the user has to
consiously make a decision to "flip" both the star base and the blue
templates over to get a S. hemi perspective. So I think it would be
good if you added radio buttons (N and S) to "flip" the blue overlay
to a S. hemi perspective similar to how the star field radio buttons
work now. This way, the analogue to using the real 2102-D would be
maintained - the user has to know which side of the star base to use
(which corresponds to knowing which radio button to use for the stars
- N or S) and also which side of the blue templates to use (which
would correspond to knowing which radio button to use for the blue
overlay - N or S). Particularly when I think of the usefulness of your
creation as a teaching tool, I am also starting to realize that the
tool should not do things automatically for the student which don't
happen with a real 2102-D, so please allow me to retract my prior
recommendation about automating the selection of the hemisphere by
using the latitude slider.


May I make a suggestion about the controls? I would propose that when
the spreadsheet opens that the available controls be:

1)"LHA Aries" - slider
2)"Star Base" - 2 Radio Buttons (N & S) (these buttons are currently
labeled N. & S. Hemisphere)
3)"Blue Template" - 3 Radio Buttons (N & S) (these would flip the blue
template)
4)"Latitude" - slider
5)"Solar Display" - 2 radio buttons (ON and OFF) (when ON, the day-of-
year slider moves the Sun)
6)"Day of Year" - slider
7)"Star Rotation" - slider (this is handy for turning the star display
so that the star names don't overlap)

For Star Rotation, a decision needs to be made whether to turn the
blue template with the stars, maintaining the LHA Aries value which is
set on the slider, or whether to keep the blue template in it's
current orientation on the screen and allow the stars to rotate
beneath it. I think the latter is preferred, and is how the graphic
display works now, but to be correct the slider should move to the new
LHA Aries as the stars are rotated (this doesn't happen in the current
spreadsheet).

Have you considered adding the red template? This might be useful for
teaching the 2102-D as well.

I'm quite interested to see if others in NAVLIST have suggestions/
observations about your creation.

Regards,
John

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