At present, several hand-held computers are available for navigation use.
They present an array of choices for the prospective buyer. Two questions
to be asked are: (1) Do I want to use a computer for navigation? and (2)
Which one should I buy?
For the first question, consider
the following facts:
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A computer will not really help you
navigate any better. The traditional method of almanac, sight reduction
tables, and chartwork will do admirably and are revered by many as being
a cornerstone of basic navigation education.
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Computer navigation is quicker, but
speed is not usually of paramount importance except in air navigation.
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A small lightweight computer will replace
several pounds of bulky books (a set of HO-229 and an almanac weigh 22
pounds).
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Under some conditions of rough weather,
or racing conditions, errors in navigation computations are a common tendency.
Computers help to minimize one's susceptibility to these errors.
So there you have
it. Is a calculator necessary? No. Is it convenient? Yes. Should one begin
learning navigation with one? Questionable. Of course if one is a math
whiz, or a computer buff, using one would seem almost irresistible.
As for the second question,
which one to buy, the following list of basic tasks which are characteristic
of navigation computers are discussed. Further discussion and the merits
of each is omitted in each individual computer description to save time
and space. Only unique assets they may have will be mentioned. Price speaks
for itself.
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SIGHT REDUCTION - This is the
key element common to all of our navigation computers. Some do it quicker
than others, but all do it well. This is what replaces 21 of those 22 pounds
of books. They compute altitude and azimuth of celestial bodies from any
location on Earth. Sight reduction represents at least 80% of the usefulness
of computers for celestial navigation.
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ALMANAC - A built-in almanac
gets rid of the other pound of books. It also saves time in having to look
up data for each celestial body observed. Some computers have almanacs
for only the sun; others for the sun and stars; and still others for the
sun, stars, and the moon and planets. In general, the more it costs, the
more you get. Bear in mind, though, that the sun is by far the most commonly
observed body.
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FIX COMPUTATION - This is the
ability to take positionlines from your observations, put them together,
and give you a fix in terms of latitude and longitude.
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RUNNING FIX - This produces a
fix from multiple observations taken at different times, and correcting
for course and speed made good between them.
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DEAD RECKONING (DR)- The computer
predicts where you will be based on course and speed entered by you.
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DRIFT - When a fix is obtained,
the computer reconciles the disparity between it and the DR position; computes
drift; and applies it to future DR positions.
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AVERAGING - Averages several
observations to minimize the effects of one faulty one. Some programs allow
you to delete a suspect observation.
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STAR IDENTIFICATION - This works
the sight reduction problem backwards to tell you the coordinates of the
star observed.
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REFRACTION - Enters corrections
for refraction, height of eye, and others. This both reminds you that they
must be allowed for, and saves having to write them down.
One final thing to consider also, any scientific calculator (i.e., one
that has trig function keys on it) can do sight reduction problems. One
may have to key in several values, or even be able to program it from a
formula in a book. But it will work, and is an often overlooked choice
to the middleground between tables and expensive turn-key computers.
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