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Two thoughts... first, the amount of error is useful in trying to
ascertain what went wrong.  If the error is a "magic number" (that is,
off by enough to suggest a transposition in digits or error of a whole
minute or degree), at least the cause is reasonably certain.  It's the
slight errors that are really annoying.  Maybe the boat moved, the body
wasn't really on the horizon, the sextant was off the vertical, a second
or two was lost in recoding the time... the list of reasons for these
small but inescapable errors can be depressingly long.

Second, I'm very reluctant to simply adjust the sight by a minute or
degree and add it to the round of sites; there is no assurance the cause
was as suggested, there's only a "good guess" as to the cause.  It helps
to remember that "Assume is the mother of all ****ups".  Assuming that
the error was "only" due to writing 45-23 for an altitude instead of
44-23 or 16:37:43 for 16:31:43 may work.  And it may not.  Better to
shoot the body several times and discard the outlier altogether(*).  In
a sense, a fix should be something of a (pleasant) surprise.  Certainly
the navigator has a sense of where the boat is, the purpose of the
sights is to determine the boat's location, not confirm the navigator's
assumptions.  After all, some assumptions can be made in error...

Rick Emerson
S/V One With The Wind

(*) Agreed that if I were in a situation with no sights or only one or
two and one of them seemed to suffer from a recording error, I'd be very
reluctant to discard it.  But I'd also have low confidence in the
resulting fix or LOP.

Bill wrote:
> Peter wrote
>
>
>> This has actually happened to me, on more than one occasion.  While
>> concentrating on the seconds, the wrong minute of time gets recorded.
>> Or while focused on the minutes of arc displayed by the sextant, the
>> wrong degree is marked (blame the scribe).
>>
>> This is also another example of why it is important to THINK about
>> what those data points mean, rather than just feeding them into some
>> blind number-crunching mathematical process.  Once plotted its obvious
>> that the point is an outlier, an apparent gross error.  But before
>> discarding the point its worthwhile checking that it is not just a
>> whole minute of time out, or a whole degree.
>>
>
> Excellent points, although it has never happened to me. 
>
> Seriously, a major outlier often turns out to be exactly as you describe, a
> minute of time or a degree of arc off. Embarrassing, but it always feel good
> to *see* the relationship, ask, "What if?" and recover the data.
>
> Bill B
>

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