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On 4/4/2012 2:39 PM, slk1000@aol.com wrote:
> but I'm more concerned about what to tell students about reducing a
> sight using a typical paper form.

Students? Don't mention it unless there is a hand waving wildly in the
air with that question.  If they are using a tabular method they have a
lot more to be concerned with. For you, knowing the v or d is 30 seconds
past the minute makes it easy to mentally interpolate using the next
minute's table for big v's like the moon.

In the bigger picture this concern is just noise given the accuracy of
the system. But if that is getting you crazy, let me push you over the edge.

If you go to the explanation pages in the almanac, it will tell you
possible error size in GHA, d and v values in the daily tables, and
their probabilities.

The Sun does have a v, but that is accounted for in the GHA of the daily
pages. For fun, note the GHA of the Sun then compare that to the GHA 48
or 96 hours later.  Is the difference 0? Or scroll down the Sun's d
column when it is, for example, 0!2.  0!2 between most hours, but
suddenly a 0!1 sneaks in!

Now consider the IC of your sextant. What is the margin of error there?
Or the accuracy along the arc of 0!2 -1!3. (That instrument error can be
measured and an adjustment table produced.)

Finally Ho, the raw sextant observation.  People average, do linear
regressions, or fit to a the actual Hc line because of random errors
there. Students on land--in real life often on the pitching deck of a ship.

If your students are using 229, then their tabular AP may be a good
distance from actual, resulting in 10-40 mile intercepts. In that case
they have to adjust for the fact their LOP is actually a Circle of Position.

And that's for one body.  Do that 2 or 3 times for other bodies,
advancing LOP's for estimated course and speed and you have your cocked
hat. Quite a while ago a long thread was to devoted to the mathematics
of the cocked hat.  Are we in it, near it, and the probabilities of the
above.

Lay that out for your students in the first session and see how many
return ;-)

Bill B

   

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