NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How Many Chronometers?
From: Greg Rudzinski
Date: 2009 Sep 15, 10:40 -0700
From: Greg Rudzinski
Date: 2009 Sep 15, 10:40 -0700
Gary, Excellent experiment. One additional thing to consider is the date of each battery. I would suggest starting with fresh batteries from the same package that are tested with a digital voltmeter before installation. It would be interesting to also compare digital watches with batteries of different ages installed. Greg On Sep 15, 2:22�am, Gary LaPookwrote: > Based on our discussion, I became curious about the accuracy of digital > watches and their suitability for use as chronometers so I went to my > local TARGET store and purchased three identical watches for $17.00 > each, the cheapest that they had. I set them and let them run for a few > days and, as I expected, they each had different rates. Based on this I > labeled them "A", "B", and "C" in the order of their rates starting with > the slowest. I then reset them to UTC at 0121 Z on May 28, 2009. I > checked them against UTC from WWV eleven days later on June 8th and > found that they were all running fast by 2, 4 and 7 seconds respectively > and I worked out their daily rates as .1818, .3636, and .6363 seconds > per day, respectively. > > On July 11th, 44 days after starting the test, the watches were fast by � > 9, 17 and 28 seconds. Using the rates determined in the first 11 days > the predicted errors would have been 8, 16 and 28 amounting to errors in > prediction of 1, 1, and 0 seconds. If using these three watches for a > chronometer we could average the three errors and end up with only a .66 > second error in the UTC determined by applying the daily rates to the > three displayed times after 33 days from the last check against WWV > which took place on June 8th. > > I determined new rates now based on the longer 44 day period of .2045, > .3864 and .6363 seconds per day, respectively. > > On September 15th at 0800 Z (per WWV), 110 days after starting the > test, �I took a photo of the watches which I have attached. The photo > shows the watches fast by 21, 41 and 69 seconds but by carefully > comparing them individually with the ticks from WWV the estimated actual > errors are 21.5, 41.8 and 69.0 seconds. Using the 44 day rates, the > predicted errors are 22.5, 42.5, and 70 seconds giving the errors in the > predictions of 1.0, 0.7 and 1.0 seconds which, if averaged, would have > caused a 0.9 second error in the computed UTC after 66 days from the > last check against WWV on July 11th. > > If, instead, I used the 11 day rates then the predicted errors would > have been 20.0, 40.0, and 70.0 seconds which would result in errors of > prediction of -1.5, -1.8, and 1.0 which, if averaged, would cause and > error in the computed UTC of -0.6 seconds after 99 days from the last > check against WWV which would have been on June 8th in this example. > > �From this experiment it appears that fifty one dollars worth of cheap > watches would give you a perfectly adequate chronometer. > > gl > > �IMG_3430.JPG > 1748KViewDownload --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---