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Dear list members,
I want to share some test results of my SNO-T.
(It was bought in Fall 2004 "new", but made in 1990,
has a factory certificate showing correction +10"
everywhere on the arc, which is nonsense, of course.
In summer 2005 I had it checked and certified by BOTH
Freiberger and Cassens-Plath. Freiberger issued a
certificate which shows the following corrections:

10d 20d 30d 40d 50d 60d 70d 80d 90d 100d 110d 120d
-4" -4" 10"  6" -1"  4"  5" -5"  4"  4"   3"   14"

Cassens-Plath wrote only their usual
"This instrument is free of errors for practical use".

However my multiple careful observations (most of them under
perfect conditions, from a balcony) indicate that there is
some arc error as well as a visible backlash.
(Of course this can always be attributed to insufficient proficiency
of the observer, but consistency of the results I obtain seem to
indicate that my proficiancy is not that bad).

In all examples below the inverting 7 x 40 scope was used,
I find it by far superior to the 3.5 x 50 Galileo scope.
Sigma stands for mean quadratic error in a series,
SD for the visible radius of the Sun.
To avoid  unconscious bias in selection
I include ALL results of the last week of which I have
accurate records.

IC from Sun, Nov. 17, average of 5 each:
clockwise: -0.42' (4SD=64.72) anticlockwise -0.16' (4SD=64.78)
sigma=0.16' in each case, true 4SD=64.8

IC from Sun, Nov. 19, average of 5 each:
clockwise or anticlockwise the same -0.4' (4SD=64.86', true 4SD=64.8')
sigma=0.15', true 4SD=64.8

IC from Sun, Nov. 20, average of 5 each:
clockwise: -0.5', anticlockwise -0.4' (4SD=65' in each case, true 4SD=64.8')
sigma=0.1'

Index from a star (Rasalhague) Nov. 20.
clockwise: -0.6', anticlockwise -0.2'.

(This is typical for my index observations from stars.
Sometimes I get -0.7 clockwise and -0.1 anticlockwise,
but the average was always
-0.4 or -0.5 during the last two weeks. In most cases I apply
the average IC=-0.4 or so.)

Deneb-Rasalhague distance, Nov. 20, 00:40 GMT
Average of 4 clockwise 51d12.0' (sigma=0.0') corrected for index: 51d11.4'
Average of 4 anticlockwise 51d11.6' (sigma=.2') corrected for index: 51d11.4'
True distance: 51d11.4'

Deneb-Rasalhague again, Nov 20, 01:00 GMT
Average of either 4 clockwise or 4 anticlockwise: 51d11.0'
Applying the average IC=-0.4' gives 51d10.6'
True distance: 51d10.7'

Deneb-Altair distance, Nov 20, 01:30 GMT
Average of 4 clockwise: 38d00.9' (sigma=0)
Average of 5 anticlockwise: 38d00.4' (sigma=0.2)
Total average of all 38d00.6'. Corrected for IC=-0.4 gives 38d00.2'
True distance: 37d59.8'
So we have 0.4' overshot.

Deneb-Altair distance, Nov 17, 01:25 GMT
Average of 6 clockwise: 38d00.8 (sigma=0)
Average of 6 anticlockwise 38d00.3 (sigma=0.3)
Total average 38d00.6' Correction for IC=-.044 gives 38d00.2'
True distance 37d59.8'
So we have overshot 0.4'

What can this be is not an arc error?

Deneb-Vega distance, Nov 20, 02:40 GMT
Average of 4 clockwise: 23d50.1 (sigma=0)
Average of 4 anticlockwise: 23d49.9 (sigma=0.1)
Total average: 23d50.0' correction for IC=-0.4 gives 23d49.6'
True distance 23d49.5'

Deneb-Vega dist., Nov 13, 23:40 GMT
Average of 4 clockwise: 23d51.3, with IC=-.8 gives 23d50.5'
Average of 4 anti-c:    23d51.0, with IC=-.4 gives 23d50.6'
True distance: 23d50.4'

Sun-Moon distance of 126 degrees, Nov. 20, 14:40 GMT corrected for IC=-0.44
Errors according to Frank's calculator: 0.3', -0.1, 0, 0.1, 0.1.

Sun-Moon distance of 137 degrees (maximum SNO arc allows! one can go
a bit further, to 141 degrees by detaching the magnifying glass:-)

Nov. 19, 14:40 GMT, corrected for IC=-0.4
Errors according to Frank's calculator: -0.2', 0.1', 0.3'.
(One blunder discarded, error 0.7')

Mars-Moon distance of 40 degrees
Nov. 18, 3:30 GMT, corrected for IC=-0.4'
Errors according to Frank's calculator: -0.3', 0.8', 0.2', 0.7', 0.7',
0.6' then checked the Frank calculator, and repeated the series, trying
to see whether I can match somehow the numbers calculator gives:-)
 -0.1', 0.5', -0.1', -0.2', -0.5',
0.3', 0.1', -0.1':-)

Mars-Moon distance at 16 degrees
Nov 13, 1:30 GMT, IC=-0.4'
Errors: 1.0', 0.6', 0.8', 0.2', 0.7'

Same, with Bill's Astra, same evening, with the SAME inverting scope:
Mars-Moon at 16 degrees, Nov 13, 1:30 GMT IC=+0.35
Errors: -0.1', 0.1', -0.1', 0.2', -0.1'

Can I conclude that my arc has a huge bump at 16 degrees?

However:
Venus-Moon November 7, GMT 0:30 at 15 degrees, IC=-0.4
Errors: -0.1', 0', 0'.

Mars-Moon distance Nov. 18 at GMT 3:20, at 40 degrees, IC=-0.4 (SNO again)
Errors: -0.1', 0.5', -0.1', -0.2', -0.5', 0.3', 0.1', -0.1'.

Sun, art horizon, oil over syrup, Nov. 20, 19:20 GMT IC=-0.4, watch exact.
Antickockwise, UL:

19:28:20  48d42.8'
19:29:50  48d25.3'
19:31:00  48d10.9'
19:32:32  47d52.9'
19:33.54  47d36.7'

Averages: 19:31:07 48d09.7'
Error: -0.2 (undershot). But actually this means -0.4 because
the measured altitude was divided by 2.

Any comments?
(I can supply more details on each observation if anyone is interested
I would be very interested to see analogous data posted (or sent to me)
by other people practicing without real horizon).

Disclaimer for George:
I understand that the issues discussed here are far from the
practical needs of a small-boat navigator:-) Still I think these are
proper questions for discussion on this list. My concern is whether
I can take reliable Lunars under good conditions from land to 0.2' precision,
and whether it is possible at all, and whether it is possible with
my SNO-T.

Alex.

   

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