NavList:

   

Reply

This is some "row statistics data" which I collected
on Bill's request. (Bill is exploring his new Astra sextant).
I thought this might be of some interest to the list members
who are interested in the hardware comparisons,
human eye performance, irradiation, and other topics that
have no direct connection with the "practical navigator needs",
when the small boat conditions and dip uncertainty
involve much larger errors.

Bill,

Using the good weather today (I am sure it is due to your
prayers:-) I made some substantial measurements with both scopes
and three sextant positions as you requested.

At 20:15 GMT (March 2) I took index measurements
with Kepler (inverting) scope: 3 measurements for each of the three
positions: upright, horizontal (handle down) and upside down.
Then at 22 GMT I repeated the same with my Galileo
(straight) scope
(5 upright, 3 horizontal and 3 upside down).
In all cases I used the same filters (2 on each mirror)

Here are the averages of the series (if the first digit to drop
in rounding is 5, I leave it). Each number below is the average
of three numbers, but in one case of 5 numbers. The total number
of observations was 20 ON and 20 OFF.

Kepler, straight       32.3   27.5 (-32.5)   64.8   +0.1
Kepler, horizontal     32.4   28.0 (-32.0)   64.5   -0.2
Kepler, upside down    32.5   28.0 (-32.0)   64.5   -0.25
Galileo, straight (5)  32.4   27.8 (-32.2)   64.6   -0.1
Galileo, horizontal    32.5   27.9 (-32.1)   64.6   -0.2
Galileo, upside down   32.4   27.6 (-32.4)   64.8    0.0

I think this shows that there is no significant difference
between the two telescopes under these conditions,
and no significant influence of sextant orientation.

Here is some more statistic based on the same data:
                   ON   SIGMA     OFF  SIGMA    4SD    CORR
All Kepler (9)     32.4 (0.12)    27.8 (0.28)   64.6   -0.1
All Galileo (11)   32.4 (0.14)    27.8 (0.23)   64.6   -0.1
All upright (11)   32.4 (0.15)    27.7 (0.26)   64.7   -0.15
All horizontal (9) 32.45(0.05)    27.7 (0.09)   64.6   -0.15
All upsidedown (9) 32.5 (0.15)    27.8 (0.29)   64.7   -0.15

The only pattern I see here is that OFF readings have for
some misterious reasons larger scattering.
Finally, assuming the true value of 2SD equal to 32.4,
the ABSOLUTE DEVIATION of 20 ON measurement was this:
0.0' (7)   0.1' (10)  0.1' (1)  0.2' (2)
and for the OFF measurements:
0.0' (0)   0.1' (4)   0.2' (6)  0.3' (3)  0.4' (4)  0.5' (3)
which shows again that OFF measurements were substantially
worse. This cannot be atributed to backlash: I rotated the drum
in both directions.

Alex.

P.S. Also I managed to take a good lunar this morning, just
before the moonset. The moon was 4d05.5' high, barely visible,
touching the trees! The Sun was 25d55' high.
The distance from the Sun to the Moon was 104 degrees.
I took the average of 3 observations and the resulting error
in the distance was 0.2' (with temperature and pressure
corrections, and using Frank's calculator)
ongitide was 6', and the error in long from the
the worst observation to 9'.

I mean the Moon alt was beyond any reasonable refraction formulas,
and the distance was pretty large. The weather was excellent though.

   

Reply