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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Watches as chronometers
From: Gary LaPook
Date: 2011 Mar 25, 01:44 -0700
 ``` This is an update on my experiment using three cheap digital watches as a chronometer. See below for prior reports and methodology.Two more sets of data have been obtained. In the format for A, B, and C in seconds: actual error; predicted error; difference.December 30, 2010, 435 days since the start:A = 101/95.4/5.6: B = 203/204.3/ -1.3: C = 347/350.7/-3.7Averaging these differences equals +0.2March 25, 2011, 551 days:A = 119/112/7: B = 234/236.4/ -2.4: C = 399/404.5/ -5.5Averaging these differences equals -.3So after 551 days, about a year and a half, the worst single error is 7 seconds making an error of 1.75 NMin longitude at the equator. Using the average of the three watches results in about a 0.3 NM error in longitude.glPrior posts:-----------------------------------------------------------------see:http://www.fer3.com/arc/m2.aspx?i=113872&y=201009 A year ago in September 2009 we discussed using cheap digital watches as chronometers in the thread "How many chronometers?" I described an experiment I was doing using three cheap (\$17.00 each) watches to determine how useful they would be as a chronometer. ( I have provided links to some of my posts in that discussion below.)The experiment has continued now for almost a year and this is an update to the prior posts.Since I had modified the test conditions temporarily to see what effect very cold temperatures would have on the rates of the watches, I had to restart the experiment on September 18, 2009, 360 days ago. The three watches, "A", "B", and "C" were, respectively, 7, 31 and 60 seconds fast at that point. I had computed their daily rates to be .1919, .3737 and .6263 seconds per day respectively. The watches are kept in a cabinet with a minimum-maximum thermometer (see photo) and the temperature range was 62.5° to 82.4° F ( 16.9° to 28.0 °C.)I have checked the watches on five occasions by comparing them with the radio time signal from WWV and estimated the time to the nearest half second. Using the daily rates, I predicted what the accumulated errors should be and compared them with the actual error and the difference would have been the error if relying on the predicted errors for navigation.The first occasion was on November 13, 2009, 56 days after the start. In the format for A, B, and C in seconds: actual error; predicted error; difference.A = 17.0/17.7/-.7: B = 52.0/51.9/ .1: C = 95.0/95.1/ -.1Averaging these differences equals -.2December 31, 2009, 104 days:A = 26.5/27.0/ -.5: B = 70.0/69.9/ .1: C = 124.0/125.1/-1.1Averaging these differences equals -.5March 16, 2010, 179 days:A = 41.0/41.3/-.3: B = 97.0/97.9/ -.9: C = 172.5/ 172.1/ .4Averaging these differences equals -.3June 23, 2010, 278 days:A = 61.5/60.3/1.2: B = 134.0/134.9/ -.9: C = 232.0/234.1/ -2.1Averaging these differences equals -.6September 13, 2010:A = 79.0/76.1/2.9: B = 164.0/165.5/ -1.5: C = 281.0/285.5/ -3.5Averaging these differences equals -.7Evaluating this data shows that the greatest difference between predicted time and actual time was 3.5 seconds after 360 days which would result in less than one minute of longitude error in almost a year. So using any one of these watches as a chronometer would provide sufficient accuracy for celestial navigation.Averaging the three readings resulted in a maximum difference of .7 seconds which would provide a longitude to an accuracy of less than one-quarter of a minute.So it appears that if the watches can be kept in the cabin where the temperature can be maintained at a comfortable temperature for the occupants, 17° to 28° C, that these three \$17 watches are all you need for a year of voyaging without recourse to a radio time signal.glCheck out these previous posts:http://www.fer3.com/arc/m2.aspx?i=109724&y=200909http://www.fer3.com/arc/m2.aspx?i=109757&y=200909http://www.fer3.com/arc/m2.aspx?i=109766&y=200909http://www.fer3.com/arc/m2.aspx?i=109824&y=200909http://www.fer3.com/arc/m2.aspx?i=109825&y=200909http://www.fer3.com/arc/m2.aspx?i=109847&y=200909http://www.fer3.com/arc/m2.aspx?i=109894&y=200909http://www.fer3.com/arc/m2.aspx?i=109942&y=200909```
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