Re: A lurker surfaces

2007-01-03 Thread Zefram
Daniel R. Tobias wrote: It's a few seconds off from TAI, isn't it? It was synchronized to UTC in 1980 (I think), Yes. The epoch for GPS time is 1980-01-06T00:00:00 UTC, which is 1980-01-06T00:00:00 GPS time. Not having leap seconds, it effectively tracks TAI, with the equation

Re: A lurker surfaces

2007-01-03 Thread Zefram
Magnus Danielson wrote: TA(GPS) = GPS + 19 + C0 No, there is no TA(GPS). TA(k) are distinct timescales that AFAICT generally do not attempt to track TAI. Presumably they are intended as maximally stable frequency standards, not steering to maintain long-term interval accuracy, like TAI itself.

Re: Wikipedia article

2007-01-03 Thread Zefram
Brian Garrett wrote: Besides, the English term leap second is a misnomer--a leap year is a year with an extra day in it (and the inserted day is *not* called a leap day) Actually it *is* called a leap day. It is the leap year terminology that is the odd one out. -zefram

Re: A lurker surfaces

2007-01-03 Thread Poul-Henning Kamp
In message [EMAIL PROTECTED], Zefram writes: Would have been nice. Actually, since the only real significance of GPS time is that it's part of the signal format, they could just as well have picked an unconventional but space-efficient encoding (say, 32-bit count of seconds, wrapping every 4

Re: Introduction of long term scheduling

2007-01-03 Thread Peter Bunclark
On Tue, 2 Jan 2007, Rob Seaman wrote: Daniel R. Tobias replies to Poul-Henning Kamp: Has anybody calculated how much energy is required to change the Earths rotation fast enough to make this rule relevant ? Superman could do it. Or perhaps he could nudge the Earth's rotation just

Re: Introduction of long term scheduling

2007-01-03 Thread Poul-Henning Kamp
In message [EMAIL PROTECTED], Peter Bunclark writes: Without the Moon, the Earth could nod through large angles, lying on its side or perhaps even rotating retrograde every few million years. Try making sense of timekeeping under such circumstances. You mean like taking a sequence of atomic

Re: Introduction of long term scheduling

2007-01-03 Thread Peter Bunclark
On Wed, 3 Jan 2007, Poul-Henning Kamp wrote: Hang on a minute, statistically planets in the Solar System do not have a large moon and yet are upright; for example Mars comes very close to the conditions required to generate a leapseconds email exploder. As far as I know the atmosphere is far

Re: Introduction of long term scheduling

2007-01-03 Thread Magnus Danielson
From: Poul-Henning Kamp [EMAIL PROTECTED] Subject: Re: [LEAPSECS] Introduction of long term scheduling Date: Wed, 3 Jan 2007 11:45:52 + Message-ID: [EMAIL PROTECTED] In message [EMAIL PROTECTED], Peter Bunclark writes: Without the Moon, the Earth could nod through large angles, lying on

Re: A lurker surfaces

2007-01-03 Thread Tony Finch
On Tue, 2 Jan 2007, Steve Allen wrote: And, yes, explaining all this is very hard. It's not obvious to the geek that the political and funding realities are more real than the underlying physics, but that's the way the world works. I've been reading The Measurement of Time by Audoin and

Re: A lurker surfaces

2007-01-03 Thread Tony Finch
On Sun, 31 Dec 2006, Rob Seaman wrote: But actually, I think we should call leap seconds what they are - intercalary events. Yes! I also liked Zefram's comment As a calendar, UTC is presently of the observational variety. http://www.mail-archive.com/leapsecs@rom.usno.navy.mil/msg01367.html

Re: Introduction of long term scheduling

2007-01-03 Thread Tony Finch
On Wed, 3 Jan 2007, Magnus Danielson wrote: Assuming you have corrected for another gravitational field, yes. The current SI second indirectly assumes a certain gravitational force, we is assumed to be at sea level whatever level that is. Wrong. The SI second is independent of your reference

Re: Introduction of long term scheduling

2007-01-03 Thread Magnus Danielson
From: Tony Finch [EMAIL PROTECTED] Subject: Re: [LEAPSECS] Introduction of long term scheduling Date: Wed, 3 Jan 2007 17:38:35 + Message-ID: [EMAIL PROTECTED] On Wed, 3 Jan 2007, Magnus Danielson wrote: Assuming you have corrected for another gravitational field, yes. The current SI

how to reset a clock

2007-01-03 Thread Tony Finch
The time APIs that I am familiar with represent time as an interval based on a fixed implicit epoch. To reset a clock that is wrong, its couner value must be set to the correct value. This implies that the system's real time clock and interval timer must be separate, so that processes depending on

Re: how to reset a clock

2007-01-03 Thread Zefram
Tony Finch wrote: Are there any APIs which have an explicit variable epoch, and which reset the clock by adjusting its epoch instead of its counter? This would eliminate the need for seperate interval and real-time clocks. Interval clock and real-time clock remain conceptually distinct. If you