building consensus
I've been reading the list archives. Parts of the discussion are rather repetetive. I think the search space could be narrowed quite a bit if the list produced a canonical statement of consensus, listing facts on which there is no dispute. This would serve much the same purpose as a FAQ, as well as possibly a base for a final report on the leap seconds issue. Let us grok in fullness before coming to a conclusion. So as a start here are some statements that I think are not controversial on this list. If any are disputed, please speak up. nature of time scales - UT1 et al are not really measures of time, but of angle (of Terran rotation). Readings of UT1 et al are most naturally represented as a real count of rotations since some epoch (i.e., as some form of Julian Date). Because TT, TAI, et al are measures of time unrelated to planetary rotation, it is misleading to apply to them the day-based notations (such as the sexegesimal time-of-day notation) that are customarily used with UT1 et al. Readings of linear time scales (TT, TAI, et al) are most naturally represented as a real count of SI seconds since some epoch. Post-1972 UTC, counting TAI seconds while maintaining a day cycle that closely matches the phase of UT1, is directly analogous to calendars that count days while maintaining a year cycle that closely matches the phase of the tropical year. Readings of UTC cannot be directly represented by a single linear count. As a calendar, UTC is presently of the observational variety. civil time -- Up to the present, most human activity has been in the long term synchronised with local solar time. We are not in a position to determine whether, to what extent, and for how long, the synchronisation between activity periods of Terran humans and the rotation of the planet will be maintained. Up to the present, local civil time has approximately maintained a conventional correspondence with the timing of human activity. By the use of standard time zones, the correspondence between local civil time and local mean solar time has historically varied within a range of about five hours, excluding arctic regions. It is presently commonplace for the correspondence between local civil time and local mean solar time to vary periodically with an amplitude of one hour. It is convenient for the civil time in different localities to have a simple relationship. Where civil time involves a unit very close in duration to the SI second, it is convenient for that to actually be the SI second on the geoid. time handling in software - Unix time, as standardised by POSIX and as commonly implemented, is a faulty encoding of UTC. The fault is that Unix time readings repeat, and so are ambiguous, near positive leap seconds. The Unix time interfaces are capable of being used to correctly encode UT1, TAI, UTC-SLS, or other time scales that do not have internally-visible leap seconds. Some applications assume that Unix time is monotonically nondecreasing, or that timestamps are unambiguous, and so are poorly served by the encoding of UTC in Unix time. Some applications assume that Unix time is a linear scale suitable for interval calculations, and so are poorly served by the encoding of any form of UT in Unix time. Some applications assume that Unix time encodes UTC, including discontinuous behaviour around leap seconds, and so would be poorly served by the encoding of anything other than UTC in Unix time. New applications need a more sophisticated understanding of time than is currently standard practice. Various applications require means to handle civil time, TAI, and UT1, among other time scales. Applications need to process times that are contemporary, historical, and in the foreseeable future, on all time scales they are interested in. When dealing with observational calendars and other unpredictable aspects of time scales, applications need a way to be sure that they have sufficiently fresh information about calendar structure. time dissemination -- Human society needs to develop better means to disseminate a multiplicity of time scales. -zefram
Re: building consensus
UT1 et al are not really measures of time, but of angle (of Terran rotation). To some degree yes, but don't they also include minor corrections (polar motion, longitude, etc.) and so at one level they already depart from raw angle measurement and instead are trying to act like clocks? /tvb
Re: building consensus
On Thu 2006-06-01T08:09:22 -0400, John Cowan hath writ: Some do, some don't, some couldn't care less. It deserves to be noted that last year at the GA in India URSI Commission J decided that it couldn't care, and discontinued its working group on the leap second. http://www.ursi.org/J_BusRepGA05.doc -- Steve Allen [EMAIL PROTECTED]WGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99858 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m
Re: building consensus
On Thu 2006-06-01T06:25:39 -0700, Tom Van Baak hath writ: UT1 et al are not really measures of time, but of angle (of Terran rotation). To some degree yes, but don't they also include minor corrections (polar motion, longitude, etc.) and so at one level they already depart from raw angle measurement and instead are trying to act like clocks? Yes. It is ironic that UT1 and UT2 were introduced in hopes of getting timeservices worldwide to finally start broadcasting time signals that agreed, but that because the observatories feeding the data to the broadcasters would not abandon the self-inconsistent values for their conventional longitudes (c.f. Janssen and Newcomb at the 1884 IMC) the signals did not start to agree until coordinated cesium clocks were in use. -- Steve Allen [EMAIL PROTECTED]WGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99858 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m
Re: building consensus
In message: [EMAIL PROTECTED] Rob Seaman [EMAIL PROTECTED] writes: : Actually, this list is not a discussion per se. If we simplify the : positions - just for the sake of argument here - to leap second yes : and leap second no, the reality is that the folks pushing the leap : second no position have never engaged with this list. There are : several doughty people here who happen to have that opinion, but they : abide with us mortals outside the time lords' hushed inner sanctum. What an amaizingly unhelpful and offsensive statement. I have spent much time explaining why leap seconds cause real problems in real applications, only to be insulted like this. Warner
Re: building consensus
M. Warner Losh scripsit: In message: [EMAIL PROTECTED] Rob Seaman [EMAIL PROTECTED] writes: : Actually, this list is not a discussion per se. If we simplify the : positions - just for the sake of argument here - to leap second yes : and leap second no, the reality is that the folks pushing the leap : second no position have never engaged with this list. There are : several doughty people here who happen to have that opinion, but they : abide with us mortals outside the time lords' hushed inner sanctum. What an amaizingly unhelpful and offsensive statement. I have spent much time explaining why leap seconds cause real problems in real applications, only to be insulted like this. I believe you have misread Rob's remark, though I concede that it was easy to misread. I believe Rob meant that the people who are pushing leap seconds no in *official* channels are not to be found on this list. That being so, the leap seconds yes folks are unable to challenge them or persuade them otherwise. You and I, on the other hand, fall into the doughty people here group. -- Is a chair finely made tragic or comic? Is the John Cowan portrait of Mona Lisa good if I desire to see [EMAIL PROTECTED] it? Is the bust of Sir Philip Crampton lyrical, http://ccil.org/~cowan epical or dramatic? If a man hacking in fury at a block of wood make there an image of a cow, is that image a work of art? If not, why not? --Stephen Dedalus
Re: building consensus
In message: [EMAIL PROTECTED] John Cowan [EMAIL PROTECTED] writes: : M. Warner Losh scripsit: : : In message: [EMAIL PROTECTED] : Rob Seaman [EMAIL PROTECTED] writes: : : Actually, this list is not a discussion per se. If we simplify the : : positions - just for the sake of argument here - to leap second yes : : and leap second no, the reality is that the folks pushing the leap : : second no position have never engaged with this list. There are : : several doughty people here who happen to have that opinion, but they : : abide with us mortals outside the time lords' hushed inner sanctum. : : What an amaizingly unhelpful and offsensive statement. I have spent : much time explaining why leap seconds cause real problems in real : applications, only to be insulted like this. : : I believe you have misread Rob's remark, though I concede that it was : easy to misread. I believe Rob meant that the people who are pushing : leap seconds no in *official* channels are not to be found on this list. : That being so, the leap seconds yes folks are unable to challenge them : or persuade them otherwise. : : You and I, on the other hand, fall into the doughty people here group. Maybe I did misread them. I've been sick the past three days, so maybe we can chalk it up to that and I'll offer my oppologies for having such a thin skin. Wanrer
Re: building consensus
Warner Losh objects:There are several doughty people here who happen to have that opinion, but they abide with us mortals outside the time lords' hushed inner sanctum.I have spent much time explaining why leap seconds cause real problems in real applications, only to be insulted like this.Sincere apologies for my awkward statement. Dictionary.com defines "doughty" as "marked by stouthearted courage; brave". I wasn't questioning the knowledge or passion of folks holding views that differ from my own. Rather I was attempting to question whether anybody actively participating on this list - holding whatever view - is also participating in ITU discussions.I see that Mr. Cowan has also parsed my admittedly opaque remarks.RobNOAO
Re: building consensus
In message: [EMAIL PROTECTED] Rob Seaman [EMAIL PROTECTED] writes: : Warner Losh objects: : : There are several doughty people here who happen to have that : opinion, but they abide with us mortals outside the time lords' : hushed inner sanctum. : : I have spent much time explaining why leap seconds cause real : problems in real applications, only to be insulted like this. : : Sincere apologies for my awkward statement. Dictionary.com defines : doughty as marked by stouthearted courage; brave. I wasn't : questioning the knowledge or passion of folks holding views that : differ from my own. Rather I was attempting to question whether : anybody actively participating on this list - holding whatever view - : is also participating in ITU discussions. : : I see that Mr. Cowan has also parsed my admittedly opaque remarks. Yes. I'm sorry I was so easily offended. Please accept my appologies for my hasty words. Warner
Re: Precision vs. resolution
Rob Seaman scripsit: Interesting question. Perhaps it is the distinction between addressability and physical pixels that one encounters on image displays and hardcopy devices? (Still have to posit which is which in that case :-) Thanks to those who responded either publicly or privately. In summary, infinite are the arguments of mages. Some take resolution to be a near-synonym for precision, some take it to be a synonym for granularity. The more definitive the source, the vaguer the definitions. I should perhaps explain that I was interested in an internal representation for durations, which I am now representing as a triple of months, minutes, and seconds (the number of minutes in a month is not predictable, nor the number of seconds in a minute given leap seconds, but all other relationships are predictable: 10080 minutes/week, 12 months/year, 100 years/century, etc.) To this I would add a fourth nonnegative integer representing clock resolution units and wanted to make sure I had the terminology correct. Ah well. -- John Cowan [EMAIL PROTECTED] http://ccil.org/~cowan In the sciences, we are now uniquely privileged to sit side by side with the giants on whose shoulders we stand. --Gerald Holton
Re: Precision vs. resolution
I should perhaps explain that I was interested in an internal representation for durations, which I am now representing as a triple of months, minutes, and seconds (the number of minutes in a month is not predictable, nor the number of seconds in a minute given leap seconds, but all other relationships are predictable: 10080 minutes/week, 12 months/year, 100 years/century, etc.) To this I would add a fourth I'm curious what motivated this particular representation given that one could perhaps also use years/days/seconds, or weeks/hours/seconds, or months/hours/seconds, or like GPS, weeks/seconds, or like MJD, days/fractions... nonnegative integer representing clock resolution units and wanted to make sure I had the terminology correct. Take this with a grain of salt since I'm still confused by resolution vs. granularity myself, but isn't the phrase clock resolution units redundant? If resolution is about the minimum unit of measure it would seem the phrase clock resolution is sufficient, no? Further, if you are counting clock cycles to subdivide integer seconds, then consider words like clock rate, or clock period, or clock granularity, or clock cycles, or just plain clock tick. That gives you months/minutes/seconds/ticks which, to me at least, sounds better than months/minutes/seconds/clock resolution units. If your clock resolution is ms or us or ns then it's even simpler, e.g., months/minutes/seconds/ns. This representation would accommodate, for example, a typical 1.193 MHz clock -- since the resolution is 1 ns while the granularity is 838 ns. /tvb
