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I found some interesting data that are relevant to several
topics discussed on this list
(like "Accuracy of altitude measurement", "Russian sextants",
"Dipmeters" etc.)
These are the accuracy data of altitude measurements with
Soviet sextants
collected by B.I. Krasavtsev and published in his book
"Marine Astronomy"
in 1986 (in Russian):

...All instrumental errors of SNO-T are less than those
of SNO-M by a factor of 2-3.

Random error of altitude measurements by the new sextant
(SNO-T) under normal conditions have standard deviation of
0.4' for the Sun and 0.5' for the stars. These data were obtained
from the scattering of series of observations.

Furthermore, in the observed altitudes, errors in the index
correction, instrumental correction, and dip correction
are unavoidable. They show as systematic errors in the
series of altitudes.
Standard deviation of this systematic error with SNO-T
is 0.4' if the dip is measured with a dipmeter, and 0.7'
if the dip is taken from the tables.

(All these data reflect statistics from Soviet merchant ships,
not the small craft).

He also confirms our guesses on what these abbreviations mean:
SNO: Sextan Navigacionnyi s Osvetitelem
(Sextant for Navigation with Illimination)
M: "Modified", T: "Tropic-resistant".

Alex.

   

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