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George Huxtable wrote:
> But now let the observer travel a few feet South, across the equator, to a
> lat of -.001 degrees South.
>
> Plugging in that new value of lat changes Z to 44.967, almost exactly the
> same as before (jst as we would expect, for such a small movement of the
> observer).

That's not what I would expect. Isn't Z measured from the pole nearest
the observer? At least, that's how HO 229 defines it. Stepping into the
Southern Hemisphere changes the scenario to "latitude CONTRARY name to
declination". That means you must use a different HO 229 page (the
facing page in the same book opening) to obtain Z. The tabulated value
is 135.0 for your example. Then apply the correct rule

>> S. Lat
>> L.H.A. greater 180..........Zn = 180-Z
>> L.H.A. less than 180........Zn = 180+Z

and all is well.

However, I never used the rules, preferring to plot directly from Z. In
your example, Z = S 135 W. On paper I find that as easy to plot as 315,
and it eliminates the Zn calculation.

   

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