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    Re: Chronometer Suggestions
    From: Gary LaPook
    Date: 2009 Jan 6, 13:15 -0800

    Make sure you go to the July 23 post not the July 25 or July 30
    posting.
    
    http://groups.google.com/group/NavList/browse_thread/thread/a270bc3d6aeb66d4?hl=en
    
    gl
    
    On Jan 6, 12:48�pm, glap...{at}PACBELL.NET wrote:
    > You don't have that exactly right, the LOP moves westward one minute
    > of arc every four seconds, not one nautical miles. Since the length of
    > one minute of longitude varies as the cosine of the latitude the
    > distance the LOP moves also varies by the cosine of the latitude. At
    > the equator the length of one minute of longitude is one nautical mile
    > but at 60� latitude it is only one half of a nautical mile.
    >
    > In addition to this, the amount of change in altitude also varies with
    > the sine of the azimuth so you have to combine these two factors. Go
    > to :
    >
    > http://navlist.googlegroups.com/attach/c09c132c9a92fad1/HO+249+extrac...
    >
    > which contains two tables called "motion of the body" or "M.O.B."
    > tables that are used in flight navigation to allow for the motion of
    > the body. Look at the table for four minutes. Since four minutes of
    > time is 60 times four seconds of time just divide the tabulated values
    > by 60 to obtain the change of altitude in four seconds of time. (Or
    > you can just consideer the tabulated values as seconds of arc.)For
    > example, the first value listed is 60' for latitude zero and azimuth
    > 90�. Go accross the top line to 60� latitude and you will find that
    > the change in altitude is 30' exactly one half of the change at the
    > equator and which would result in a change of 30 NM in the intercept.
    >
    > Go to my July 30, 2008 post on the "Celestial up in the air" thread
    > for further explanation at :
    >
    > http://groups.google.com/group/NavList/browse_thread/thread/a270bc3d6...
    >
    > gl
    >
    > On Jan 6, 12:20�pm, "Federico Rossi" 
    > wrote:
    >
    > > Lu,
    >
    > > If I�ve understood well, this error doesn�t depend on your latitude on
    > > earth, i.e. it�s a maximum of 1 nm for every 4 seconds (for bodies due east
    > > or west) whether you are on the equator or far from it, does it?
    >
    > > Federico
    >
    > > Da: NavList@fer3.com [mailto:NavList@fer3.com] Per conto di
    > > Lu Abel
    > > Inviato: marted� 6 gennaio 2009 20.05
    > > A: NavList@fer3.com
    > > Oggetto: [NavList 6941] Re: Chronometer Suggestions
    >
    > > Irv and Bill:
    >
    > > It's a MAXIMUM of 1 NM for every 4 seconds, not a minimum. �
    >
    > > If the body you're sighting is directly north or south of you, even a fairly
    > > significant time error would result in a very minimal shift in the LOP
    > > produced by the body (the extreme example is Polaris). � On the other hand,
    > > if the body you're sighting is directly east or west, then it's Geographic
    > > Position is moving by 1 NM every four seconds and any LOP developed from
    > > that sight would be off by 1 NM for every four seconds of clock error.
    >
    > > Lu Abel
    >
    > > Irv Haworth wrote:
    >
    > > Minimum of 1 NM for every 4 seconds..( a quick answer)..
    >
    > > Irvin F Haworth
    >
    > > W, Van BC Canada
    >
    > > � _____ �
    >
    > > From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf
    > > Of William Sellar
    > > Sent: January 6, 2009 5:05 AM
    > > To: NavList@fer3.com
    > > Subject: [NavList 6931] Re: Chronometer Suggestions
    >
    > > As a beginning celestial navigator, I am wondering how much time and watch
    > > accuracy is actually required for practical navigation. �Can we predict how
    > > many miles off one would be for every second of time error?
    >
    > > Bill
    >
    >
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