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Hi Brad,

It looks absolutely great.

Your explanation of setting up for plotting a planet is ingenious.
That would be a valuable addition.

There is another feature required for the red template. The red
template needs it's own slider for SHA rotation, and will need a
numeric readout of the SHA of the red index line (the line with the
slot in it on a 2102-D). In other words, it needs to be independently
rotatable from the blue template and have it's own LHA readout as
well.

Here is why: in addition to plotting planets & moon, there is another
use for the red template. It requires that you use both the red and
blue on the star base at the same time.

Let's say you are taking a round of sights on an evening with heavy
broken clouds. You have got a sight to the north and one to the WSW
and now need one to the ESE so that you will get good separation and a
nice "cocked hat" when you plot the LOPs. You preset your sextant for
the nav star in the ESE that you had pre-planned, but you look to take
the sight and there is a cloud in the way. Your pre-planned alternates
are also blocked by clouds. But there is a star visible a few degrees
higher - you know it is not one of the 57 nav stars because you wrote
all those down for that part of the sky (and of course you know the 57
by heart) and you know where the planets are so it is not one of them
either. But the horizon is fading fast so you take the shot on it
noting the time of course but also the bearing to the unknown star.
Now back to the 2102-D. You mount the blue template and set it for the
LHA Aries for your DR longitude at the time of the sight. Now you
mount the red template on top of the blue, and holding the blue in
place, you rotate the red template so that the index line (with the
slot) pases directly over the altitude and azimuth of your unknown
star (altitude from your sextant reading, azimuth from the bearing you
took). Now read the Declination of your star from the concentric
cirles on the red template that pass nearest that
altitude/azimuth (interpolate as needed). The red index line will
indicate an LHA - subtract this number from 360 to get the SHA of your
star. Then you check the star table in the Nautical Almanac that lists
173 stars - if you could see the star when the horizon was visible, it
will almost certainly be one of these. Look for a star with an SHA and
Dec matching what you got from the red template. When you find one
very close, you have identified it and can use the more precise info
from the almanac to proceed to reduce the sight. This procedure is
contained in Dutton's.

Once you add this and your planet/moon plotting, I think it will be
complete.

Navlist - anything we are missing?

Regards,
John
Tokyo, Japan
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