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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Quartz Watch Movement Replacement
From: Bill B
Date: 2012 Jun 18, 20:00 -0400
From: Bill B
Date: 2012 Jun 18, 20:00 -0400
On 6/18/2012 6:53 PM, Greg Rudzinski wrote: > To time to the tenth of a second is best done directly with the > shortwave and split/stopwatch. There is a fractional delay when using > non video still camera images. The camera clock is only + 0.5 seconds > precision or so where the stopwatch is good to a hundredth of a second. > Your video technique should be good to 3/100 of a second if everything > is synchronized. Greg The way I figure it at 30 fps the increments are 1/30 or 0.033 seconds. I did check the frame rate against a stop watch. Perhaps we are on different pages or my explanation was lacking. I am not using the camera clock at all. I simply place the two displays side by side and video about 5 seconds worth. Then I can playback advancing (or backing up) frame by frame. For example if I am using the NIST computer display as a standard I can watch it change over to a new second and then count how many frames it takes a slow watch's display to catch up. 5 frames is 5/30 or 0.17 seconds slow. As to trusting my eye vs reflex time and/or sound ticks vs sight, I do not have that much faith in myself. NIST claims about 0.2 second is the best we can distinguish. Based on my results I believe that. I was rather amazed that it could take up to 5 frames for my RCC's large digits to completely change the second in certain combinations! I cannot see it, but the camera does. If my eyes were better that would make a strong case for an analog display. The most disappointing results were from my Garmin 76. In an article Garmin engineers stated that Garmins run 1/2 to 1 second slow as the chip spends the majority of its energy on the position/time computations rather than the time display. They also stated 1 to 2 seconds delay for Lowrance, and did not mention Magellan etc. In my observations the Garmin would actually advance 2 seconds at a time with a weak signal; skipping the intermediate second completely. Even with strong horizon-to-horizon satellite views it would often "stack" seconds--a quick change from one to the next then a relatively long delay before the next change over. I have not yet been able to discern if the average time lag from UTC is constant/predictable. As for my RCC that was the subject of so much supposition after Alex and I observed together, it has been put through every torture test I can devise without destroying it, is viewed approximately 40 times daily, and has never so much as hiccuped. It is spot on after its 2 AM EDT reset. My only problem with it is a 0.9 second drift (slow) over the 24 hours between resets. Voluntary standards would have it within plus/minus 0.5 seconds of UTC at any time. Fortunately the drift rate is constant, so easy to mentally adjust to UT1--until the June 30 leap second ;-) Bill B