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    Re: Navy MK 5 Octant Using Natural Horizon
    From: Alexandre Eremenko
    Date: 2012 May 2, 16:40 -0400

    Here is my series: MkIXA, bubble, 19:50-20:03 GMT, Sun altitude errors
    (no refraction correction made, just compare what I read with the true
    -1'4, +5, -0'5, 0'5, -0'9, -4'5, -0'5, -1'4.
    And then the Sun disappeared:
    The average error of these is -0.46,
    and refraction correction is -0'6.
    So if I do take refraction into account I was 1' off.
    And the spread is 9'5 :-(
    In your longer series the spread is 7'2, if I read your numbers correctly.
    The question of standartization of terminology was raised.
    I am curious how aviators called the altitude (angle)
    to distinguish from the altitude which is in feet:-)
    Is this a standard practice in US Cel Nav to write
    "A" and "T" AFTER the number
    instead of + or - BEFORE the number,
    as most of the rest of the world does ?
    And to use this weird abbreviation 3' moa instead of just writing 3' ?
    What else 3' can mean in Cel Nav context? Three feet?
    It took me some time to figure out what this "moa" in your messages
    stands for:-)
    OK, Sun is comng back:-)
    On Wed, 2 May 2012, Greg Rudzinski wrote:
    > Alex,
    > I thought you might be interested in the last 32 bubble horizon observations 
    (without averager) using the Navy MK 5 in perfect conditions from the 
    stability of my boat dock. I'll let you crunch the numbers. Various bodies 
    Sun, Moon, Planet, Stars observed over the last few weeks.
    > 0.6T 0.8A 2.1A 0.1T 0.8A 4.6A 1.6A 0.1A 0.5A 1.7T 1.2A 0.5T
    0.1T 0.5A 2.7T 2.9A 0.2A 0.3T 2.2A
    > 2.1A 2.0T 2.7A 1.7T 2.6T 3.4A 2.4T 1.7T 2.3T 1.0T 2.0T 3.2A 3.7A
    > Did I use the correct index correction ;-)  +2  moa I.C. for the bubble horizon.
    > Greg Rudzinski
    > NavList] Re: Navy MK 5 Octant Using Natural Horizon
    > From: Alexandre Eremenko
    > Date: 1 May 2012 18:17
    > Greg,
    >> The results are not extraordinary in that any data set from
    >> any sextant can be made to look good by adjusting the index error.
    > Does your octant have adjustment for the index error?
    > I understand that with ordinary sextants the index error can be
    > adjusted. The problem is to determine it with 0.2 accuracy:-)
    > Besides, we know that even good ordinary sextants can have substantial
    > arc error, etc. Which is again hard to find.
    > Now, the 0.2 average error in your 30 observations shows that the
    > index error as you determined it is very close to the truth.
    > Did you adjust it? I supose not, (otherwise why would you adjust
    > it to 6')
    >> is why I look at the maximum and minimum values of a set
    >> of data to judge a sextant and or navigator performance.
    > The maximum spread of 2.7 shows that the errors are all less then
    > 1.2 or 1.4 in magnitude.
    > But you did not answer my question: how did you choose the preset values?
    > And why they were such as we see them.
    > Alex.
    >> Keep an eye open on ebay for U.S. Navy MK 5's which can be
    >> had for under $100 but use caution on the buy.
    > I don't know how can one "use caution" with a sextant on e-bay,
    > especially with an air sextant:-)
    > You can only take the risk.
    > 99.9% of e-bay sellers would say in advance that they know nothing about
    > sextants, which is true, about half of them photograph a normal sextant
    > upside down. Once I asked a seller what is the radius of the arc, and his
    > reply was that he is not sure what the "radius" is :-)
    > So I do not expect them to answer such questions as whether the bubble is
    > present or not. I simply thought that $100 or $140 that I payed is a sum
    > I can afford to risk:-)
    > I was lucky: the only thing which did not work was the light,
    > and I found how to fix it and fixed in few hours.
    > But repairing a bubble is definitely beyond my possibilities:-(
    > Alex.
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