Re: [LEAPSECS] drawing the battle lines
In message e1uagid-000nir...@stenn.ntp.org, Harlan Stenn writes: Warner, I think your position is only valid form the point of view that says a timescale can only be used to count fixed-length seconds. That is not really what timescales are about. Timescales, as concept, are for communicating unambiguously the duration of the time interval between two or more events. Given the many and varied circumstances of human lives, it follows that many kinds of timescales are in routine use, from counting to 'safe days' to splitting pico-seconds for science. Most of these timescales are local, they apply only to one particular woman or one particular experimental setup in a lab. The coordinated in UTC is all and only about, through international coordination, providing a timescale which is local to the entire planet, in order to enable world-wide communication about events on a global scale. It should come as no surprise that such a timescale originated from the TELCO community, when international communications boomed. It follows pretty obviously, that the important thing about UTC is that everybody can agree what time it is, with a trivial overhead spent on coordination Thanks to improvements in timekeeping technology and computer networking, leap-seconds now impede communication rather than aid it, because you can't predict them more than 6-8 months ahead, and they have a unreasonable cost of coordination. Either the cost and impediment to communication must be reduced vastly, or leapseconds must go, because the benefit they provide is utterly marginal. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
I think the problem is that time scale is not defined. It could be a scale that can be used both to indicate when events occurred or will occur, and to find durations by subtracting the beginning time from the ending time, and during any duration of the same number of seconds, physical processes such as the cycles emitted by an atomic clock will progress to the same degree. But it could instead refer only to a scale used by people to record events and plan for future events, without any implication that two durations that are nominally the same number of seconds will have physical processes progress to the same degree. UT1 is satisfactory for most event recording and planning purposes. Gerard Ashton -Original Message- From: leapsecs-boun...@leapsecond.com [mailto:leapsecs-boun...@leapsecond.com] On Behalf Of Harlan Stenn Sent: Wednesday, May 08, 2013 10:36 PM To: Leap Second Discussion List Subject: Re: [LEAPSECS] drawing the battle lines (Found unsent in my Drafts folder...) Warner Losh writes: I think the real reason that UT1 shouldn't be considered a time scale is that it is based on not an imperfect realization of a fixed length second, but rather an imperfect realization of a variable (measured by oscillations of a fixed frequency) length second. Warner, I think your position is only valid form the point of view that says a timescale can only be used to count fixed-length seconds. If one considers a timescale as a counting of days it's a bit different. Then we get to look at leap years, and the adjustment made at the beginning of the Gregorian calendar. Would it be appropriate to say that these issues are more about 'cardinal' v. 'ordinal'? And then, if you are on one side of the issues, the other side is clearly wrong. Look at how badly people got leap year calculations wrong before Y2K. H ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
(Found unsent in my Drafts folder...) Warner Losh writes: I think the real reason that UT1 shouldn't be considered a time scale is that it is based on not an imperfect realization of a fixed length second, but rather an imperfect realization of a variable (measured by oscillations of a fixed frequency) length second. Warner, I think your position is only valid form the point of view that says a timescale can only be used to count fixed-length seconds. If one considers a timescale as a counting of days it's a bit different. Then we get to look at leap years, and the adjustment made at the beginning of the Gregorian calendar. Would it be appropriate to say that these issues are more about 'cardinal' v. 'ordinal'? And then, if you are on one side of the issues, the other side is clearly wrong. Look at how badly people got leap year calculations wrong before Y2K. H ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
On Mar 20, 2013, at 11:46 PM, Rob Seaman wrote: On Mar 20, 2013, at 8:28 PM, Joseph Gwinn joegw...@comcast.net wrote: True enough, but beside my point. The relationship between UTC and UT1 is piecewise linear between leap seconds, so there are steps in the first derivative at the joints between lines,and steps in zeroth and first derivatives at the leap seconds. Ignoring the perpetual refrain about leap seconds being merely a representational issue, Kevin's question was about point 9 of the CCTF recommendation, which is an assertion about UT1 itself. Saying UT1 is unacceptable as a time scale is like saying John Harrison's descendants should refund the longitude prize. Many quantities can serve as timelike independent variables. Our notion of what constitutes a time scale has evolved over time. When John Harrison won the prize, this was the best we could do. We can do better now. Nobody is saying that Darwin's On The Origin of the Species should be recalled because some of the details of the Theory of Evolution have been corrected and refined by science in the intervening years. But it occurred to me that beside the point. I think the real reason that UT1 shouldn't be considered a time scale is that it is based on not an imperfect realization of a fixed length second, but rather an imperfect realization of a variable (measured by oscillations of a fixed frequency) length second. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
On Wed, 20 Mar 2013 22:46:01 -0700, Rob Seaman wrote: On Mar 20, 2013, at 8:28 PM, Joseph Gwinn joegw...@comcast.net wrote: True enough, but beside my point. The relationship between UTC and UT1 is piecewise linear between leap seconds, so there are steps in the first derivative at the joints between lines,and steps in zeroth and first derivatives at the leap seconds. Ignoring the perpetual refrain about leap seconds being merely a representational issue, Kevin's question was about point 9 of the CCTF recommendation, which is an assertion about UT1 itself. Saying UT1 is unacceptable as a time scale is like saying John Harrison's descendants should refund the longitude prize. Many quantities can serve as timelike independent variables. I'm just summarizing what I think the ITU intended to say. Arguing that the ITU is wrong in what they said does not change the translation. It's pretty clear that ITU intends to make UTC essentially like TAI, but not just as a paper clock. If ceasing leap seconds would manage this transmogrification from paper clock to real clock, than simply applying DTAI manages the same thing. I was just observing what their direction appears to be. I don't have a vote in the ITU. And I will say that in the big radars I build, leap seconds are a real problem, one that we solve by using GPS System Time in all but human interfaces. So you recognized that UTC did not match your project requirements and used a different widely available time scale that did. How exactly were you disadvantaged? The disadvantage was that many people believe UTC to be suitable, but don't notice or deal with the leap seconds, which is devastating in radar trackers for instance. With one dish radar system, we were forced to use UTC because a major piece of reused software couldn't handle conversion between GPS System time and UTC, and so needed to run only UTC. To verify if this would work, we artificially inserts both plus and minus time steps of one second. Adding a second caused no visible disturbance. Subtracting a second caused some gyrations, but these soon dissipated. The dish rotation period was 12 seconds, so one second is almost 10% error in the detection timestamps, and this was enough. A faster rotating radar would not have been able to handle such a step discontinuity. The ITU is attempting to turn one flavor of time scale into another. The fallacy is the notion that we shouldn't have two time scales in the first place. Well, standards groups do do these things, and over time it is a great help. I would look to the history of machine screw threads for a parallel. In my case, ceasing to have leap seconds will be helpful. In your case, it's not helpful. This is also true of all standards, which are thus decided by the balance. Joe ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
Rob Seaman sea...@noao.edu wrote: Saying UT1 is unacceptable as a time scale is like saying John Harrison's descendants should refund the longitude prize. I think a better analogy is saying 1/10,000 of the distance between a pole and the equator is not an acceptable standard length. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ Forties, Cromarty: East, veering southeast, 4 or 5, occasionally 6 at first. Rough, becoming slight or moderate. Showers, rain at first. Moderate or good, occasionally poor at first. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
I'm still puzzled at the reasons for stating that UT1 should not be considered as a time scale in this recommendation. How does that serve this recommendation? This is a bit of a different question from evaluating UT1 as a time scale. Instead, it is a question about the reasons why the evaluation of UT1 must be included in this recommendation. Does saying that UT1 is not a time scale strengthen the other points in any way? Is it necessary for the other points to be accepted? Best, Kevin Kevin K. Birth, Professor Department of Anthropology Queens College, City University of New York 65-30 Kissena Boulevard Flushing, NY 11367 telephone: 718/997-5518 We may live longer but we may be subject to peculiar contagion and spiritual torpor or illiteracies of the imagination --Wilson Harris Tempus est mundi instabilis motus, rerumque labentium cursus. --Hrabanus Maurus Warner Losh i...@bsdimp.com Sent by: leapsecs-boun...@leapsecond.com 03/21/13 02:14 AM Please respond to Leap Second Discussion List leapsecs@leapsecond.com To Leap Second Discussion List leapsecs@leapsecond.com cc Subject Re: [LEAPSECS] drawing the battle lines On Mar 20, 2013, at 10:45 PM, Harlan Stenn wrote: So I gotta ask. What's the problem with doing radar and other similar things in GPS time and keeping human time in UTC, with leap seconds? I mean, sure, years ago timestamps were YYMMDDHHMMSS and those eventually got bigger, and eventually folks started noticing that things really got interesting twice a year jumping in and out of daylight savings time. But doesn't that mean that we can solve the problem even better by making sure folks use timestamps that contain the timescale when that level of effort is useful? Three things: (1) Leap seconds are rarely done correctly, and even when done correctly come at a cost that is disproportionate to their value. (2) You can know GPS time without knowing UTC, but not vice versa, since you have to know the GPS UTC offset, which isn't knowable until after the first almanac download, especially for a cold GPS receiver. (3) There will be much confusion as the two type of time are mixed. Note that there is no daylight savings time in UTC, so that part of the argument can be ignored. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
Rob Seaman sea...@noao.edu wrote: 10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second; This is irrelevant and is meant to imply that any issues with implementing a redefined UTC will be minor. They will not be minor for my community. I gathered from the report of the meeting that the IAU is happy with the idea of abolishing leap seconds. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ Forties, Cromarty: East, veering southeast, 4 or 5, occasionally 6 at first. Rough, becoming slight or moderate. Showers, rain at first. Moderate or good, occasionally poor at first. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
There's a lot of overlap between timekeepers and astronomers. I'm not sure I embrace the battle metaphor, but if so this would have to be a civil war. The fundamental issue remains that atomic time and synodic time are two different things. Thus the BIPM's implicit attempt to divorce the word day from its current coherent meaning. Steve's issues won't go away if UTC is redefined. Rather confusion would ramify and reify. Systems, software and society need to characterize dates as coherently as they do times. Dates and times are for many purposes the same thing (else you wouldn't query them with an atomic system call). If the BIPM now states otherwise, then what does day mean to them? Perfection of means and confusion of goals seem, in my opinion, to characterize our age. - A. Einstein, 28 September 1941 Rob Seaman National Optical Astronomy Observatory -- On Mar 20, 2013, at 6:46 AM, Steve Allen s...@ucolick.org wrote: The BIPM website has a few new tidbits related to UTC. They celebrate 25 years since the BIH was abolished, TAI was transferred from BIH to BIPM, and Circular T was started. They also celebrate one year since starting the new UTCr. And they have published the report of the 19th meeting of the CCTF http://www.bipm.org/utils/common/pdf/CCTF19.pdf in which there is a long discussion of the UTC shenanigans at ITU-R. Concluding the report is Resolution 6 in which the CCTF declares what UT1 is and is not, what UTC is, and what a time scale is in a fashion that directly contradicts the 1976 IAU definition of time scale. In particular, resolution 6 makes it plain that the count of days in a calendar and the subdivision of those days is not a time scale if those days are measured by astronomical means. In short, that history, tradition, law, and common public perception about what time is have been wrong. -- Steve Allen s...@ucolick.orgWGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165Lat +36.99855 1156 High StreetVoice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
I can understand points 1 through 8, 10, and 11, but . . . What is gained by point 9 stating that UT1 should not be considered as a time scale? Kevin Kevin K. Birth, Professor Department of Anthropology Queens College, City University of New York 65-30 Kissena Boulevard Flushing, NY 11367 telephone: 718/997-5518 We may live longer but we may be subject to peculiar contagion and spiritual torpor or illiteracies of the imagination --Wilson Harris Tempus est mundi instabilis motus, rerumque labentium cursus. --Hrabanus Maurus Warner Losh i...@bsdimp.com Sent by: leapsecs-boun...@leapsecond.com 03/20/13 11:17 AM Please respond to Leap Second Discussion List leapsecs@leapsecond.com To Leap Second Discussion List leapsecs@leapsecond.com cc Subject Re: [LEAPSECS] drawing the battle lines On Mar 20, 2013, at 7:46 AM, Steve Allen wrote: The BIPM website has a few new tidbits related to UTC. They celebrate 25 years since the BIH was abolished, TAI was transferred from BIH to BIPM, and Circular T was started. They also celebrate one year since starting the new UTCr. And they have published the report of the 19th meeting of the CCTF http://www.bipm.org/utils/common/pdf/CCTF19.pdf in which there is a long discussion of the UTC shenanigans at ITU-R. Concluding the report is Resolution 6 in which the CCTF declares what UT1 is and is not, what UTC is, and what a time scale is in a fashion that directly contradicts the 1976 IAU definition of time scale. In particular, resolution 6 makes it plain that the count of days in a calendar and the subdivision of those days is not a time scale if those days are measured by astronomical means. In short, that history, tradition, law, and common public perception about what time is have been wrong. A secular understanding of time is to a scientific time scale as a biblical understanding of origins is to scientific evolution theory. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
In message a72f135c-ce3f-48df-bc61-6ab4e68e7...@noao.edu, Rob Seaman writes: There's a lot of overlap between timekeepers and astronomers. There's a lot of overlap between bioinformatics and ornitology. Was there any relevant point you were trying to make ? The fundamental issue remains that atomic time and synodic time are two different things. The IAU and CCTF seems to be absolutely clear on the difference: A) Atomic time is time. B) Earth orientation is geometry. The fact that we used to estimate time from Earth orientation does not give astronomers some kind of hereditary claim to forever control our timescales. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
Hi Kevin, I can understand points 1 through 8, 10, and 11, but . . . What is gained by point 9 stating that UT1 should not be considered as a time scale? Well, then, let's examine the text in question (bold, underline and italics in original - don't know if French and English are regarded as equally normative): RECOMMENDATION CCTF 6 (2012) A contribution from the Consultative Committee on Time and Frequency (CCTF) on achieving a continuous reference time scale The CCTF, having analyzed the terms of WRC-12 Resolution 653 adopted by the World Radiocommunication Conference (WRC) 2012 on the Future of Coordinated Universal Time (UTC) which invites the ITU WRC 2015 to “consider the feasibility of achieving a continuous reference time-scale, whether by the modification of UTC or some other method and take appropriate action, taking into account ITU-R studies,” and instructs the ITU Secretary-General “to bring this Resolution to the attention of relevant organizations such ... the General Conference on Weights and Measures (CGPM), the Consultative Committee for Time and Frequency (CCTF), the Bureau International des Poids et Mesures (BIPM) …” So they are responding to the ITU's language, but likely many of the same individuals were instrumental in the focus on the word continuous. UTC is, of course, a continuous time scale already. Leap seconds are a representational issue. Recommends that the following facts be recognized in the implementation of a continuous time scale: Not sure what it means to recommend the recognition of a fact, but empiricists since Descartes would likely not disagree. The question is whether the following statements are facts. 1. a continuous time scale is indeed achievable, and that it has been realized and maintained by the International Bureau of Weights and Measures; Stipulated to within the limits of current metrology. 2. a continuous reference time scale corresponds to UTC without leap second discontinuities; And also corresponds to UTC with leap seconds. There are no discontinuities. 3. the concepts of continuity and uniformity should be applied strictly in a reference time scale; This is not a fact, it is a statement of policy and requires detailed definition. 4. the unit for any quantity in metrology is unique, and as such, a single time scale should also be unique; Two things. The SI-second is derived from a more fundamental frequency standard. There are and will remain vast numbers of time scales that are directly or indirectly layered on the SI-second. 5. in the event of a redefinition of any quantity in metrology, the unit should be invariant, and particularly for the second of the Système International the respective scale should be continuous and uniform; This scale already exists in TAI. If TAI has issues, it isn't obvious why UTC needs to be changed. Does TAI actually have issues? It is an opinion, not a fact, to assert that practical time scales need be uniform. And uniform with respect to what? 6. the name “Coordinated Universal Time” be maintained in the case of a redefinition of UTC without leap second adjustments; This is an opinion, not a fact. Many disagree with their opinion. 7. the term “Universal” in “Coordinated Universal Time” implies that the time scale is to be used throughout the world; No. There is no term Universal in Coordinated Universal Time. Rather UTC parses as Coordinated Universal Time. Universal Time is a prior term that has always been approximately equivalent to Greenwich Mean Time. Relying on sophistry in definitions reflects a weak underlying position. 8. the term “Coordinated” in “Coordinated Universal Time” implies coordination among National Metrology Institutes and not a relationship to the direction of the Sun from a position on the surface of the Earth; The second half of this sentence belongs with Universal Time. Again, definitions are not facts. 9. the angle UT1 used to relate celestial and terrestrial reference systems should not be considered as a time scale, but as the angle that characterizes the variable rotation of the Earth; UT1 can be both an angle and a time scale. That the rotation of the Earth and other bodies varies does not invalidate the identification of the word day with synodic day. 10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second; This is irrelevant and is meant to imply that any issues with implementing a redefined UTC will be minor. They will not be minor for my community. 11. a wider dissemination of UT1-UTC is to be
Re: [LEAPSECS] drawing the battle lines
On Mar 20, 2013, at 2:20 PM, Rob Seaman wrote: 2. a continuous reference time scale corresponds to UTC without leap second discontinuities; And also corresponds to UTC with leap seconds. There are no discontinuities. discontinuities here means irregularity not the a violation of the contrived continuity of the variable radix UTC. 3. the concepts of continuity and uniformity should be applied strictly in a reference time scale; This is not a fact, it is a statement of policy and requires detailed definition. Viewed from a fixed-radix standard, a leap second is a discontinuity and a non-uniformity. 4. the unit for any quantity in metrology is unique, and as such, a single time scale should also be unique; Two things. The SI-second is derived from a more fundamental frequency standard. There are and will remain vast numbers of time scales that are directly or indirectly layered on the SI-second. 5. in the event of a redefinition of any quantity in metrology, the unit should be invariant, and particularly for the second of the Système International the respective scale should be continuous and uniform; This scale already exists in TAI. If TAI has issues, it isn't obvious why UTC needs to be changed. Does TAI actually have issues? It is an opinion, not a fact, to assert that practical time scales need be uniform. And uniform with respect to what? TAI isn't disseminated. 6. the name “Coordinated Universal Time” be maintained in the case of a redefinition of UTC without leap second adjustments; This is an opinion, not a fact. Many disagree with their opinion. 7. the term “Universal” in “Coordinated Universal Time” implies that the time scale is to be used throughout the world; No. There is no term Universal in Coordinated Universal Time. Rather UTC parses as Coordinated Universal Time. Universal Time is a prior term that has always been approximately equivalent to Greenwich Mean Time. Relying on sophistry in definitions reflects a weak underlying position. 8. the term “Coordinated” in “Coordinated Universal Time” implies coordination among National Metrology Institutes and not a relationship to the direction of the Sun from a position on the surface of the Earth; The second half of this sentence belongs with Universal Time. Again, definitions are not facts. 9. the angle UT1 used to relate celestial and terrestrial reference systems should not be considered as a time scale, but as the angle that characterizes the variable rotation of the Earth; UT1 can be both an angle and a time scale. That the rotation of the Earth and other bodies varies does not invalidate the identification of the word day with synodic day. UT1 is a time realization of an angle. It is an irregular time scale because it is based on an imperfect oscillator whose frequency error and time error are not predictable. That's what makes it not a suitable times scale. 10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second; This is irrelevant and is meant to imply that any issues with implementing a redefined UTC will be minor. They will not be minor for my community. If you take the product of inconvenience and probability of that inconvenience summed over all users, you'll find the change has a low expected impact. 11. a wider dissemination of UT1-UTC is to be encouraged; Again, a policy, not a fact (whether or not desirable). and further recommends that the International Committee for Weights and Measures (CIPM) and the International Telecommunication Union – Radiocommunication Sector (ITU-R) consider the formation of a joint working group to study the possibility of coordinating future actions in the definition of the continuous world-reference time scale. This may well be a good idea, but perhaps additional institutions should be involved? The function of point 9 (in combination with others such at #5) is to argue that civil timekeeping doesn't need to remain tied to Earth rotation. Rather, the fact is that time in society depends on both atomic and synodic time scales. To control Universal Time (as opposed to Universal Time) they first must argue that a single time scale can rule them all. It is not obvious why TAI does not already fill this role. And if not TAI, define some other continuous time scale (by whatever definition of continuous) under a different name, and leave UTC (~ GMT) alone. TAI is a paper clock. It has no real-time realization. UTC is a real-time realized clock, and has traceable chains of time transfers. Warner
Re: [LEAPSECS] drawing the battle lines
On Mar 20, 2013, at 2:29 PM, Warner Losh i...@bsdimp.com wrote: TAI isn't disseminated. Well, yes it is. From ITU-R TF.460-6: E DTAI The value of the difference TAI – UTC, as disseminated with time signals, shall be denoted DTAI. DTAI = TAI − UTC may be regarded as a correction to be added to UTC to obtain TAI. The TAI − UTC values are published in the BIPM Circular T. The IERS should announce the value of DTAI in integer multiples of one second in the same announcement as the introduction of a leap-second (see § D.2). TAI / DTAI could certainly be distributed better than implicitly through Bulletin C (http://data.iers.org/products/16/15458/orig/bulletinc-045.txt), but the two time scales address different needs. Removing access to UT (~ GMT) does not in itself improve access to TAI. UT1 is a time realization of an angle. It is an irregular time scale because it is based on an imperfect oscillator whose frequency error and time error are not predictable. That's what makes it not a suitable times scale. The proposition seems beyond silly, for it implies that there were no time scales before the invention of the atomic clock. - a wise person who eschews this arena. 10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second; This is irrelevant and is meant to imply that any issues with implementing a redefined UTC will be minor. They will not be minor for my community. If you take the product of inconvenience and probability of that inconvenience summed over all users, you'll find the change has a low expected impact. Boeing didn't expect their batteries to go up in smoke either. By all means the CCTF should explore the risk matrix, having taken it on themselves to recommend a change. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
I would propose that ITU is using continuity and uniformity in their mathematical definitions, implying that the intent is that at least in definitional theory, UTC be mathematically continuous with all its derivatives (noise being ignored). This would exclude step discontinuities (leap seconds) and piecewise linearity (like UT1). Given that the length of a SI second is constant, what's left is a UTC that is a constant offset from TAI, where the offset changes only if so ordered. Joe From: Warner Losh i...@bsdimp.com To: Leap Second Discussion List leapsecs@leapsecond.com Date: 03/20/2013 05:35 PM Subject:Re: [LEAPSECS] drawing the battle lines Sent by:leapsecs-boun...@leapsecond.com On Mar 20, 2013, at 2:20 PM, Rob Seaman wrote: 2. a continuous reference time scale corresponds to UTC without leap second discontinuities; And also corresponds to UTC with leap seconds. There are no discontinuities. discontinuities here means irregularity not the a violation of the contrived continuity of the variable radix UTC. 3. the concepts of continuity and uniformity should be applied strictly in a reference time scale; This is not a fact, it is a statement of policy and requires detailed definition. Viewed from a fixed-radix standard, a leap second is a discontinuity and a non-uniformity. 4. the unit for any quantity in metrology is unique, and as such, a single time scale should also be unique; Two things. The SI-second is derived from a more fundamental frequency standard. There are and will remain vast numbers of time scales that are directly or indirectly layered on the SI-second. 5. in the event of a redefinition of any quantity in metrology, the unit should be invariant, and particularly for the second of the Système International the respective scale should be continuous and uniform; This scale already exists in TAI. If TAI has issues, it isn't obvious why UTC needs to be changed. Does TAI actually have issues? It is an opinion, not a fact, to assert that practical time scales need be uniform. And uniform with respect to what? TAI isn't disseminated. 6. the name “Coordinated Universal Time” be maintained in the case of a redefinition of UTC without leap second adjustments; This is an opinion, not a fact. Many disagree with their opinion. 7. the term “Universal” in “Coordinated Universal Time” implies that the time scale is to be used throughout the world; No. There is no term Universal in Coordinated Universal Time. Rather UTC parses as Coordinated Universal Time. Universal Time is a prior term that has always been approximately equivalent to Greenwich Mean Time. Relying on sophistry in definitions reflects a weak underlying position. 8. the term “Coordinated” in “Coordinated Universal Time” implies coordination among National Metrology Institutes and not a relationship to the direction of the Sun from a position on the surface of the Earth; The second half of this sentence belongs with Universal Time. Again, definitions are not facts. 9. the angle UT1 used to relate celestial and terrestrial reference systems should not be considered as a time scale, but as the angle that characterizes the variable rotation of the Earth; UT1 can be both an angle and a time scale. That the rotation of the Earth and other bodies varies does not invalidate the identification of the word day with synodic day. UT1 is a time realization of an angle. It is an irregular time scale because it is based on an imperfect oscillator whose frequency error and time error are not predictable. That's what makes it not a suitable times scale. 10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second; This is irrelevant and is meant to imply that any issues with implementing a redefined UTC will be minor. They will not be minor for my community. If you take the product of inconvenience and probability of that inconvenience summed over all users, you'll find the change has a low expected impact. 11. a wider dissemination of UT1-UTC is to be encouraged; Again, a policy, not a fact (whether or not desirable). and further recommends that the International Committee for Weights and Measures (CIPM) and the International Telecommunication Union – Radiocommunication Sector (ITU-R) consider the formation of a joint working group to study the possibility of coordinating future actions in the definition of the continuous world-reference time scale. This may well be a good idea, but perhaps additional institutions should be involved? The function
Re: [LEAPSECS] drawing the battle lines
On Mar 20, 2013, at 6:02 PM, Joseph M Gwinn gw...@raytheon.com wrote: I would propose that ITU is using continuity and uniformity in their mathematical definitions, implying that the intent is that at least in definitional theory, UTC be mathematically continuous with all its derivatives (noise being ignored). This would exclude step discontinuities (leap seconds) and piecewise linearity (like UT1). Given that the length of a SI second is constant, what's left is a UTC that is a constant offset from TAI, where the offset changes only if so ordered. Relative to what? If UT1 is an angle, then derivatives with respect to angular time are stationary, and derivatives with respect to atomic time vary. At any rate, continuous is still the wrong word. All the derivatives of sin(t) are continuous, but the function itself is non-monotonic. Leap seconds are a means to an end. Earth does not exist in a vacuum (well, it does :-) but Earth is not the only example we have. There are 25 terrestrial worlds in the solar system - 4 planets, 2 dwarf planets interior to Pluto, 19 large moons - and on each day means synodic day. This includes fast and slow, prograde and retrograde and synchronous rotators. Io and Europa actually move non-monotonically (making little backward loops) in their shared orbit with Jupiter. And on each there is one fewer solar day per year than sidereal rotations. It's disingenuous to argue that the functional form of civil time - calendar and clock time - doesn't follow mean solar time, angle or not, varying or not. By all means we can discuss alternative ways to solve the problem. But this will only be successful if the problem is cast in a coherent fashion. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
On Wed, 20 Mar 2013 20:16:49 -0700, Rob Seaman wrote: On Mar 20, 2013, at 6:02 PM, Joseph M Gwinn gw...@raytheon.com wrote: I would propose that ITU is using continuity and uniformity in their mathematical definitions, implying that the intent is that at least in definitional theory, UTC be mathematically continuous with all its derivatives (noise being ignored). This would exclude step discontinuities (leap seconds) and piecewise linearity (like UT1). Given that the length of a SI second is constant, what's left is a UTC that is a constant offset from TAI, where the offset changes only if so ordered. Relative to what? If UT1 is an angle, then derivatives with respect to angular time are stationary, and derivatives with respect to atomic time vary. At any rate, continuous is still the wrong word. All the derivatives of sin(t) are continuous, but the function itself is non-monotonic. True enough, but beside my point. The relationship between UTC and UT1 is piecewise linear between leap seconds, so there are steps in the first derivative at the joints between lines,and steps in zeroth and first derivatives at the leap seconds. No trig functions need apply. It's pretty clear that ITU intends to make UTC essentially like TAI, but not just as a paper clock. And I will say that in the big radars I build, leap seconds are a real problem, one that we solve by using GPS System Time in all but human interfaces. Joe ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] drawing the battle lines
So I gotta ask. What's the problem with doing radar and other similar things in GPS time and keeping human time in UTC, with leap seconds? I mean, sure, years ago timestamps were YYMMDDHHMMSS and those eventually got bigger, and eventually folks started noticing that things really got interesting twice a year jumping in and out of daylight savings time. But doesn't that mean that we can solve the problem even better by making sure folks use timestamps that contain the timescale when that level of effort is useful? H ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
