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    Re: What do "d" and "v" really stand for?
    From: Greg R_
    Date: 2008 Jun 19, 23:07 -0700

    Correct - the "d" and "v" corrections (among other things) were new
    items that I had to learn when I picked up celnav again a couple of
    years ago and decided to join the rest of the nautical world in using
    the Nautical Almanac.
    
    --
    GregR 
    
    
    --- glapook---.net wrote:
    
    > 
    > Except that there are no "v" or "d" corrections with the Air Almanac
    > since the period between tabulated data is only ten minutes and, to
    > the accuracy of that almanac and in flight CN, there is no loss by
    > ignoring such slight changes for such a short interpolation period.
    > 
    > gl
    > 
    > On Jun 19, 11:52 pm, "Greg R."  wrote:
    > > --- glap...---.net wrote:
    > > > "v, the difference between the actual change in GHA in one hour
    > and a
    > > > constant value used in the interpolation tables; and d, the
    > change in
    > > > declination in one hour."
    > >
    > > Right, those tell what "v" and "d" are (and like I think anyone
    > who's
    > > reduced sights manually would know what they are) - but my original
    > > question was what actual words the letters are abbreviations for.
    > >
    > > BTW, I originally learned celnav with the Air Almanac (way back in
    > the
    > > mid-70s - at the time it looked "easier" than using the Nautical
    > > version), but I'd be totally lost if I had to use it now...  ;-)
    > >
    > > --
    > > GregR
    > >
    > > --- glap...---.net wrote:
    > >
    > > > Look at article 1903 in Bowditch, available here:
    > >
    > >
    >
    http://www.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-19.pdf
    > >
    > >
    > >
    > > > "v, the difference between the actual change in GHA in one hour
    > and a
    > > > constant value used in the interpolation tables; and d, the
    > change in
    > > > declination in one hour."
    > >
    > > > gl
    > >
    > > > On Jun 19, 10:41 pm, glap...---.net wrote:
    > > > > Here are excerpts from the 1937 N.A The first page shows the
    > time
    > > > of
    > > > > transit of the moon of the Greenwich meridian and contains a
    > "Var.
    > > > per
    > > > > hour" column, variation?, the change in declination inone
    > hour."
    > >
    > > > >http://www.geocities.com/fredienoonan/almanac-1937-136.JPG
    > >
    > > > > The second page contains moon data showing GHA and DEC and has
    > > > > separate increments tables for each day based on the the dec
    > change
    > > > > and GHA change rates for that particular day. no "v" or "d"
    > > > correction
    > > > > factors are shown.
    > >
    > > > >http://www.geocities.com/fredienoonan/almanac.html
    > >
    > > > > This third link takes you to a site I put up with with excerpts
    > of
    > > > > various navigation texts.
    > >
    > > > >http://www.geocities.com/fredienoonan/
    > >
    > > > > gl
    > >
    > > > > On Jun 19, 9:00 pm, frankr...{at}HistoricalAtlas.net wrote:
    > >
    > > > > > Greg, you asked:
    > > > > > "And maybe that's going to be about as good an answer as we
    > can
    > > > hope for
    > > > > > at this point in time - does anyone know when "d" and "v"
    > terms
    > > > first
    > > > > > showed up in the NA as such? There might be more elaboration
    > > > about what
    > > > > > the abbreviations stood for when they were first introduced."
    > >
    > > > > > Yes, that's basically what I was providing you in the
    > previous
    > > > message. The
    > > > > > labels "v" and "d" first appear in the "Abridged Nautical
    > > > Almanac" in 1952.
    > > > > > This is the earliest date when the official British almanac
    > > > included GHA.
    > > > > > This had been introduced 18 years earlier in the American
    > > > Nautical Almanac,
    > > > > > and it was also widely used in the various air almanacs. As I
    > > > said, the
    > > > > > concept of the interpolation constant at the foot of each
    > column
    > > > on the
    > > > > > almanac page was already present in the American almanac
    > where it
    > > > was called
    > > > > > a "code". I also checked a couple of commercial British
    > almanacs
    > > > from this
    > > > > > period (the commercial British almanacs adopted GHA well
    > before
    > > > the official
    > > > > > British almanac). They use a similar principle but again not
    > > > labeled v and
    > > > > > d. So my best guess right now is that the first use of these
    > > > specific labels
    > > > > > for the interpolation data is the British "Abridged Nautical
    > > > Almanac" in
    > > > > > 1952. Here's the full text from the explanation in the AbNA
    > for
    > > > 1953:
    > > > > >  "Interpolation between the tabulated hourly values is
    > provided
    > > > for by
    > > > > > comprehensive interpolation tables, printed on coloured pages
    > at
    > > > the end of
    > > > > > the book, giving for every minute and every second the
    > increments
    > > > of G.H.A.
    > > > > > corresponding to the mean rate of increase for the Sun (15�
    > > > precisely), the
    > > > > > constant rate for Aries (15� 02'.46) and the minimum rate for
    > the
    > > > Moon (14�
    > > > > > 19'.0). The variations from the means are so small for the
    > Sun
    > > > that they
    > > > > > have been deliberately ignored; the tabulated hourly values
    > of
    > > > the Sun's
    > > > > > G.H.A. have been adjusted so that the error thus caused is a
    > > > minimum. These
    > > > > > variations cannot be ignored for the planets or for the Moon,
    > and
    > > > > > corrections have to be made for the excess (v) in hourly
    > motion
    > > > over that
    > > > > > adopted in the main interpolation tables."
    > >
    > > > > > So there's an answer: v stands for "excess". :-)
    > >
    > > > > > In the next paragraph:
    > > > > > "The corrections for these VARIATIONS [...] are taken
    > directly
    > > > from the
    > > > > > interpolation tables with argument v" and "A similar
    > procedure is
    > > > used to
    > > > > > interpolate the declinations of the Sun, Moon and planets;
    > here
    > > > d, the
    > > > > > hourly DIFFERENCE, is given without sign on the daily pages"
    > (I
    > > > have
    > > > > > capitalized those two words for emphasis). So if you must
    > assign
    > > > a meaning
    > > > > > to v and d, I think the best bets are "variation" (of the
    > rate of
    > > > change of
    > > > > > GHA from the selected mean rate) and "difference," but the
    > catch
    > > > is that the
    > > > > > person who wrote this explanatory section may very well have
    > > > invented those
    > > > > > origins on the spot.
    > >
    > > > > > By 1958, when the modern Nautical Almanac was formed by the
    > > > merger of the
    > > > > > American Nautical Almanac and the Abridged Nautical Almanac
    > (they
    > > > kept their
    > > > > > separate names until 1960), the explanation simply refers to
    > v
    > > > and d values
    > > > > > with no hint of any etymology. Same in Bowditch of the same
    > era.
    > > > I think
    > > > > > this is intentional. The labels v and d really are not
    > intended
    > > > to "stand
    > > > > > for" anything.
    > >
    > > > > >  -FER
    > > 
    > 
    
    
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