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The Index error remained fixed during the day at 2.5' since this morning. I
adjusted it this evening to a smaller value, well after all the sights were
taken. The watch is fine - a brand new Casio GLX-5600 G-Shock which loses
time at a constant rate of 0.2 of a second per day and was -2.0 seconds all
day today.

BTW, what is the difference between
a) a blunder in calculations,
b) a blunder in calculations,
???

-----Original Message-----
From: Alexandre Eremenko
Sent: Wednesday, March 28, 2012 9:24 PM
To: zvidoron@btinternet.com
Subject: [NavList] Re: Sudden shift in sextant sights

Zvi,

1. Have you tried to check the index error before and after the shift?
You do not mention this in your message.

2. I suppose you watch is not an "atomic" one :-)
so a sudden shift in your watch is excluded.

3. let me cite from the recently mentioned article by Lt. Logan, US Navy,
"Exceptional navigational refraction near the horizon":

"The horizon and sun remaining visible, the altitude shown by the sextant
had almost instantly to be altered 32' to maintain contact, the horizon
appeared to fall by that amount..."

If you think that causes in 1 and 2 are excluded, you can read more
about 3 in the recent discussion "Extremely poor conditions???"
on this list:-)

As always, I would try to look for the simplest possible explanation
a) a blunder in calculations,
b) a blunder in calculations,
c) a blunder in time recording or in the reading of the scale.
d) that something has happened with the sextant. (Checking index correction
before and after the observations helps).

Alex.
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