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    Re: Timekeeping and sight time records
    From: Victor Garand
    Date: 2005 Mar 17, 07:33 -0700

    Having kicked off this topic with a question about a particular wrist watch
    a few days ago, I feel responsible for the possibility that we may have
    wandered off List subject to some extent.
    
    My understanding is that the general area of interest is
    astronomical/celestial navigation in the classical sense and as the final
    level of reliability.
    
    As we all know, accurate timekeeping is one of the primary requirements for
    celestial navigation at sea and it hasn't changed much for quite some time.
    When I was first introduced to the subject (over 50 years ago), this
    requirement was met through the use of two high quality mechanical
    chronometers mounted on gimbals and padded for shock protection. These were
    kept in the chartroom and set to GMT. They were wound at the same time and
    the same way every day and daily records of cumulative errors were kept
    (based on past performance records). Periodic performance checks were
    usually based on HF radio time signals (these were so widely accepted by
    then that "lunars" were considered the stuff of master navigators). I can't
    recall the error rates which could be expected from the mechanical
    chronometers but it seems they were quite small (as the fellow said, "when I
    was young,  adults were so much taller than they are today").
    
    In any case, today's needs are met with a set of two wrist watches
    (chronometers - quartz),  an error log and a multi-band radio receiver which
    will operate from batteries or a 12 volt DC source (not much change from the
    past except for the very low error records). A third wrist watch has been
    added (chronometer - quartz) which is solar powered and receives the WWVB
    signal. This last one has a push button time recorder feature which is
    proving to be very handy in recording sight times (you can record the time
    without taking your eye away from the sextant telescope). An important final
    time related item is of course Bruce Stark's Lunar tables!
    
    The sighting platform is usually a modest sailing sloop (35 to 45 feet). On
    board computer access to the web is not an option (except in some ports).
    
    From a practical standpoint, GPS is used extensively and the notebook
    computer is loaded with Garmin's "Map Source - Blue Chart". That however may
    be a subject for another List.
    
    By the way, if you need an excuse to spend time on the subject of celestial
    navigation, don't forget that the GPS network is a DoD facility. I
    understand that general access is officially at the discretion of DoD
    (national emergencies etc. could change the situation). Celestial navigation
    can therefore still be considered the final back-up.
    
    Thanks to all who commented.
    
    P.S. A miniature atomic clock the size of a pencil eraser is under
    development at NIST. Assuming eventual mass production and low cost, this
    would provide the ultimate independent time source to the navigator. See,
    http://tf.nist.gov/ofm/smallclock/index.htm
    
    Vic Garand
    
    
    ----- Original Message -----
    From: "Craig" ;
    To: 
    Sent: Wednesday, March 16, 2005 7:59 PM
    Subject: Re: Timekeeping and sight time records
    
    
    > Thank you.  In my previous message I referred to software which does
    > exactly that, accommodates the delays, but I'll restate:
    > it is the luck of the draw; you may hit 4 or 5 times with only a ms delay,
    > but then the next might be 2 s.  If you set it to
    > synchronize every minute (a waste of time ha,ha) you will get a reset
    > practically every minute due to these variances as well
    > as poor time keeping with your average computer clock.  Old proverb: A man
    > with one watch knows what time it is; a man with
    > two is never quite sure...
    >
    > Craig
    >
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Jared Sherman
    > Sent: Wednesday, March 16, 2005 13:31
    > To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
    > Subject: Re: [NAV-L] Timekeeping and sight time records
    >
    >
    > Craig, you might want to look for a freeware app called TimeRC3 (.exe or
    > .zip) which not only accomodates the propogation delays, but displays the
    > delay times it finds on the main screen. Very slick and stable little app,
    > and if you sync three or four times in a row and it shows only millisec
    > delays each time...you can be pretty sure the clock is set better than
    > you'll ever need to know. You can't "click" a button with the human hand
    > and
    > get that precision, much less read and note clock time that well.
    
    
    

       
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