NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Use of a stopwatch to time celestial sights
From: Gary LaPook
Date: 2009 Sep 22, 03:48 -0700
From: Gary LaPook
Date: 2009 Sep 22, 03:48 -0700
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 --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---