Difference between revisions of "Wall clock PPM"
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The clock was started at 2010-03-01 12:00:02, it was set to 12:00:00, but I am slow, the 2 seconds have been acounted for in the results below: | The clock was started at 2010-03-01 12:00:02, it was set to 12:00:00, but I am slow, the 2 seconds have been acounted for in the results below: | ||
− | 2010-03-02 15:34:00 - 4 seconds ahead => 40. | + | 2010-03-02 15:34:00 - 4 seconds ahead => 40.31ppm |
− | 2010-03-11 18:11:00 - 70 seconds ahead => 78. | + | 2010-03-11 18:11:00 - 70 seconds ahead => 78.98ppm |
− | 2010-03-29 17:39:00 - 140 seconds ahead => 57. | + | 2010-03-29 17:39:00 - 140 seconds ahead => 57.39ppm |
Notice how the human error is minimized. | Notice how the human error is minimized. | ||
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Set time: 2010-01-29 17:42:20 a delay of 1 sec was introduced (slow mofo) | Set time: 2010-01-29 17:42:20 a delay of 1 sec was introduced (slow mofo) | ||
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+ | 2010-01-30 17:37:00 - 5 seconds ahead => 55.75ppm | ||
/Goofy | /Goofy |
Revision as of 16:40, 30 March 2010
PPM - A Layman approach to accurate measurements
The wall clock had been running too fast for a long time, about 10min, I wondered how much. Well I could use a stop-watch and count how long it takes to count 60sec. The problem with this is that the uncertainty of my reaction speed would have a significant impact on the result. Say I can react within 1 sec, that is also the resolution on the watch, the potential error is 1/60, or 16667PPM!! (OMG,BBQ,WTF and so on and so forth).
The solution was simple but brilliant (in all modesty).
As a time reference, the clock on National Television channel DR1's Teletext. The accuracy of this clock is not known to me, but it is most likely sync'ed to DCF77 or similar.
The time of sample was done by reading the clock at at certain time based on the time on the TV. The delay of up to 1 sec. still exsists, but I now have a "stop-watch" that can run for so long, that the 1sec is a very low factor in the overall result.
The results
The clock was started at 2010-03-01 12:00:02, it was set to 12:00:00, but I am slow, the 2 seconds have been acounted for in the results below:
2010-03-02 15:34:00 - 4 seconds ahead => 40.31ppm
2010-03-11 18:11:00 - 70 seconds ahead => 78.98ppm
2010-03-29 17:39:00 - 140 seconds ahead => 57.39ppm
Notice how the human error is minimized.
Watch was then reset according to TV channel, as DST is in effect now. New readings will be posted, once enough time has past :-)
Set time: 2010-01-29 17:42:20 a delay of 1 sec was introduced (slow mofo)
2010-01-30 17:37:00 - 5 seconds ahead => 55.75ppm
/Goofy