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    Re: Use of a stopwatch to time celestial sights
    From: Greg Rudzinski
    Date: 2009 Sep 22, 16:09 -0700

    Gary,
    
    When I was younger there wasn't a problem with remembering the time of
    an observation but now my short term memory is not so good so the stop
    watch has become  standard equipment in the sextant box. The stop
    watch is very helpful in twilight conditions to preserve the time .
    Some use the sextant light to illuminate the watch but I find the
    brightness lacking. Another use of the stopwatch is for rating and
    comparing watches to the tenth of a second.
    
    Greg
    
    On Sep 22, 3:48�am, Gary LaPook  wrote:
    > 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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