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>
>But that would still leave us with the problem of what happens when the
>cocked hat chances to be very small or very large. Can you explain how
>the probability remains at 0.25?
>
>
Trevor.

Thankyou for your posting in which you find some accord with my answer to
the question, "How often will my actual position be enclosed by the cocked
hat resulting from the plotted bearings on three landmarks?"

As you point out, there are other ways in which this question can put and
which do not actually mean the same think. However, from a practical
navigators point of view, it is worth knowing that the answer to THIS
question is one time in four.

Coming to your question above where you are concerned that even when the
cocked hat is very small, how can it be that the probability remains at 0.25?

If I may say so, I think that this question is the result of trying to put
too much statistical significance on one cocked hat. If you did three more
measurements on the same landmarks and drew another cocked hat, the size of
the cocked hat would not be the same. When plotted on the chart the cocked
hat might not even be in the same place, as I have shown.

If the bearings are repeated many times so that a series of cocked hats
could be drawn on the chart, then we could make some statistical conclusions.

The first is that the actual position would be somewhere in the center of
the distribution of cocked hats.

The second is that the level of confidence with which we know the centre of
the distribution (the actual position) will increase as the square root of
the number of cocked hats.

The third is some cocked hats will be large, some small. But the size of
distribution of cocked hats will give us some information on the accuracy
of our bearing measurements.

For these cocked hats to be "independent" so that we may make arrive at the
statistical conclusions outlined above, the measurements made for one
cocked hat cannot be used for any other cocked hat.

One more point. The cocked hats for the two classes of cocked hat which
will always enclose the actual position, will tend to be larger than the
cocked hats for the other six classes which can never enclose the actual
position. Small cocked hats should be treated with suspicion!

Geoffrey Kolbe.

   

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