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    Re: Use of a stopwatch to time celestial sights
    From: Brad Morris
    Date: 2009 Sep 22, 23:31 -0400

    Hi Gary
    
    Deck watches (essentially mechanical stop watches, with the same rattrapante 
    feature described below) were used to transfer the time from the chronometer 
    to the time of observation.  No sense in moving the chronometers from snug 
    chambers.    Here is an example of one on eBay, right now
    
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280399930771
    
    As you properly note, an inexpensive digital watch can do the same function.  Maybe not as much fun!!
    
    Best Regards
    Brad
    
    
    ________________________________________
    From: navlist@fer3.com [navlist@fer3.com] On Behalf Of Gary LaPook [glapook@pacbell.net]
    Sent: Tuesday, September 22, 2009 6:48 AM
    To: NavList@fer3.com
    Subject: [NavList 9849] Use of a stopwatch to time celestial sights
    
    The same can be done with any cheap digital watch with a stopwatch
    function. They allow you to take many "lap" times just by pushing a
    button which you can read later. Reset the stopwatch and then start it
    running and write down the clock time. Then just press the "lap" button
    for each shot. At the end of all the shots simply recall the "lap times"
    from the memory and add them to the start time to establish the times of
    the shots.
    
    
    
    gl
    
    
    
    
    Brad Morris wrote on May 14, 2009:
    
    
    And speaking of navigation and time....
    
    For a very long time, I was puzzled by Dutton's recommendation to navigators 
    that they obtain a split seconds watch.  He described two second hands.  One 
    would continue to beat time, the other would pause and hold the time whilst 
    it was recorded.  I search far and wide for a "split seconds" watch of this 
    type.  I am very pleased to report to the list that such a watch should have 
    the complication known as "rattrapante".  When you search on eBay for this 
    type of watch, you immediately get listings describing exactly what Dutton 
    recommended.
    
    I somehow managed to obtain one.  Am I ever pleased!  The rattrapante 
    chronograph I obtained holds not only the seconds, but the hours and minutes 
    and tenths of a second as well. All of the hands are analog.  I have set the 
    rattrapante complication to GMT, while the normal analog watch is set to my 
    local time zone. Upon observation, I reach with my left hand to my right 
    wrist and press the button.  Now the altitude and time correspond and can be 
    recorded at leisure.
    
    I have been carefully rating the rattrapante against the USNO time, 
    (202)-762-1069 here in the US.  The rate is 0.200 seconds per day, when rated 
    over the past 20 days.  Each day, the USNO time is compared to the 
    rattrapante, and the resultant error is recorded.  Since the tenths of a 
    second is the resolution, I should continue more than 50 days to eliminate 
    any quantizing error. If the rate is not precisely 0.2 seconds, then as the 
    accumulation of short or long rate continues, eventually, there will be an 
    advance or retreat that holds.
    
    I thought it relevant to report the name to others who might wish to obtain 
    the watch recommended by the US Navy for celestial navigation.  Dutton, after 
    all, was the text used at the Academy!
    
    Best Regards
    Brad
    
    
    
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