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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Watches as chronometers
From: Geoffrey Kolbe
Date: 2013 Jun 15, 21:36 +0100
That it the point I have been trying to push all along Paul.
If you have chronometer - which will be used for navigation purposes to derive geographical positions of celestial bodies using the Nautical Almanac or equivalent ephemerides - and you wish to rate that chronometer, then you need to rate it against a UT1 time source, not a UTC time source. What is the point of rating it against UTC...?
UT1 is not just approximated by UTC, it can be obtained from UTC to the nearest millisecond.
UT1 = UTC + DUT1 where DUT1 is the difference between UT1 and UTC. There are websites which give the current and historic information for DUT1, which is given to the nearest millisecond. In principle then, it is possible to obtain UT1 to the nearest millisecond.
So, at the start of your rating period, look up the current value of DUT1, apply that correction to WWV or broadcast time and note the difference of your chronometer to that corrected time.
At the end of your rating period, look up the current value of DUT1, apply that correction to WWV or broadcast time and note the difference of your chronometer to that corrected time.
Ignore any leap second corrections that have been applied in the meantime to UTC.
Repeat, no matter how short (two seconds) or long (ten years) the rating period is, ignore any leap seconds that have been applied to UTC in the meantime.
Geoffrey Kolbe
From: Geoffrey Kolbe
Date: 2013 Jun 15, 21:36 +0100
I disagree, Geoffrey. Like Gary, I periodically compare clocks to UTC (WWV) and log the results. It is not the same as comparing to UT1.
That it the point I have been trying to push all along Paul.
If you have chronometer - which will be used for navigation purposes to derive geographical positions of celestial bodies using the Nautical Almanac or equivalent ephemerides - and you wish to rate that chronometer, then you need to rate it against a UT1 time source, not a UTC time source. What is the point of rating it against UTC...?
UT1 is not just approximated by UTC, it can be obtained from UTC to the nearest millisecond.
UT1 = UTC + DUT1 where DUT1 is the difference between UT1 and UTC. There are websites which give the current and historic information for DUT1, which is given to the nearest millisecond. In principle then, it is possible to obtain UT1 to the nearest millisecond.
So, at the start of your rating period, look up the current value of DUT1, apply that correction to WWV or broadcast time and note the difference of your chronometer to that corrected time.
At the end of your rating period, look up the current value of DUT1, apply that correction to WWV or broadcast time and note the difference of your chronometer to that corrected time.
Ignore any leap second corrections that have been applied in the meantime to UTC.
Repeat, no matter how short (two seconds) or long (ten years) the rating period is, ignore any leap seconds that have been applied to UTC in the meantime.
Geoffrey Kolbe
