NavList:

   

Reply

On May 28, 2005, at 10:13 AM, Alexandre Eremenko wrote:

> Fred,
> Sorry. I made a typo as always:-(
> This time in the date of the second observation:
> the correct date is May 28, that is this morning.
> (I computer the altitudes two times before posting them:-)
>
>
>> First, I think it's great that Alex is getting
>> observations that are
>> within 0.1' or 0.2' of arc from his known position,
>>
>
> Why do you say "within 0.1' or 0.2' ?"
> The error is less than 0.1', but with the typo uncorrected it is
> 6.6' as you say:-))

I just assumed there was a blunder somewhere and that your
calculations were correct.

>> One would think that adjusting the backlash
>> on the sextant wouldn't
>> have affected the readings as long as one always
>> approached the final
>> setting from the same direction.
>>
>
> As I said, I am not sure what they adjusted, though I saw
> the whole procedure, because
> we could not properly communicate.
>
>
>> One psychological explanation may be that Alex finally became
>> confident enough in his instrument and himself
>>
>
> This cannot be an explanation.
> I have no doubt that my sextant had some strange bias
> always in the same direction, of variable magnitude
> and range about 0.3'-0,6'.
>
> You used it yourself once with the result +0.3' off with
> art horizon (which is really equivalent to +0.6'.
> I understand that your single measurement proves nothing
> but I have two large notebooks full of observations
> taken in October-May.
> Something WAS wrong with this sextant though I don't
> know exactly what it was.
>

I was judging from my own experience.  Suddenly, one day, I was able
to get precise and accurate sights, consistently.

I am conjecturing the same thing happened with you since we can't
seem to come up with a physical explanation for the large readings
you experienced prior to the adjustment of the instrument.  I would
welcome a physical explanation based on some adjustment of the
instrument; this psychological one is the only alternative I can
imagine, and it's not entirely satisfactory.

By my calculations with your two sets of sights, the mean and
standard deviation of Ho-Hc in minutes of arc were 0.096 +/- 0.195
and 0.032 +/- 0.137.  Were your previous sights this precise?

   

Reply