Re: [LEAPSECS] Future time
Poul-Henning Kamp wrote: > In message <52dc19ff.9499.11a39...@dan.tobias.name>, "Daniel R. Tobias" > writes: > > >When I'm making an advance dinner reservation for 7 PM on October 1, > >2014 in New York City, I expect that [...] > > That used to be the "sensible party position", but it breaks down > in heaps once you start to schedule tele-conferences etc. In theory it works fine, if it is done properly. The organiser needs to pick a primary location, where the local time of the appointment remains fixed. There might be some secondary locations if some participants are elsewhere; these are useful for automatically displaying the correct time of the appointment for each person, and for the organiser to spot if their proposed time happens to be 04:00 for one of the participants. The secodary locations are also useful when a TZ rule change occurs: the scheduler can find all the appointments that are affected by the rule change, that is, appointments that occur in multiple locations where the TZ rule change affects the locations differently. This kind of automated assistance is impossible if you schedule in UTC. If you schedule in a fixed zone (whether fixed UTC offset, or fixed local time rules, or fixed Olson tz name) there are situations where a rule change will invalidate your scheduling. However current scheduling software requires you to schedule in this broken way because the main calendaring data format (iCalendar) has the wrong data model. So in practice it is impossible to schedule things in a way that is robust against TZ changes. There are other problems with existing calendaring software such as getting time zone names wrong, e.g. implying the time zone in Lisbon in the summer is called GMT. So in practice scheduling in UTC makes sense. Longer version of this argument: http://fanf.livejournal.com/104586.html Tony. -- f.anthony.n.finchhttp://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] Future time
Warner Losh wrote: > On Jan 18, 2014, at 1:52 PM, Stephen Scott wrote: > > The basis of my understanding is that UTC is a timescale that: > > -progresses at a rate of the second (SI) and has done so since > > 1972-01-01. > > -is expressed as a count in the form of date, hours, minutes and > > seconds; > > -is continuous other than the discontinuities resulting from leap > > second corrections; > > To pick a pedantic nit: It is continuous. No "other than". UTC is a > continuous time scale. It has a non-uniform radix that is expressed at > the leap seconds when its rules for labeling seconds changes slightly to > label the leap second 23:59:60. The timescale has a discontinuity when > there's a phase jump. UTC does not have phase jumps, even if it chooses > a non-traditional time to label some of its seconds once every year and > a half or two. I think it is reasonable to say that UTC's labelling of seconds is discontinuous. For timescales that use simple ancient sexagesimal notation you can write down some straightforward formulae mapping between a count of seconds and a broken down time. If you try to do the same for UTC you have to write down something that is piecewise linear with exceptions. It isn't a continuous map like other timescales. Tony. -- f.anthony.n.finchhttp://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] Future time
On Jan 20, 2014, at 10:27 AM, Tony Finch wrote: > Warner Losh wrote: >> On Jan 18, 2014, at 1:52 PM, Stephen Scott wrote: > >>> The basis of my understanding is that UTC is a timescale that: >>> -progresses at a rate of the second (SI) and has done so since >>> 1972-01-01. >>> -is expressed as a count in the form of date, hours, minutes and >>> seconds; >>> -is continuous other than the discontinuities resulting from leap >>> second corrections; >> >> To pick a pedantic nit: It is continuous. No "other than". UTC is a >> continuous time scale. It has a non-uniform radix that is expressed at >> the leap seconds when its rules for labeling seconds changes slightly to >> label the leap second 23:59:60. The timescale has a discontinuity when >> there's a phase jump. UTC does not have phase jumps, even if it chooses >> a non-traditional time to label some of its seconds once every year and >> a half or two. > > I think it is reasonable to say that UTC's labelling of seconds is > discontinuous. For timescales that use simple ancient sexagesimal notation > you can write down some straightforward formulae mapping between a count > of seconds and a broken down time. If you try to do the same for UTC you > have to write down something that is piecewise linear with exceptions. It > isn't a continuous map like other timescales. UTC defines second labeling such that it isn't technically discontinuous. It is an irregular radix that requires non-naieve math to properly convert to a count. UTC broke with thousands (or at the very least hundreds[*]) of years of time keeping practice by making what had been a completely regular radix notation for the time and converted to an irregular radix with known rules, but no known schedule. Still a pain no matter what you call it. Warner [*] An interesting side note about days: The ancient Egyptians regarded light and night as two separate realms rather than as being two halves of the same day. The notion of the synodic day thus dates only from the new kingdom, somewhere around 1400BC where the two different realms, each governed by 12 starts was replaced by a system that unified them under 24 stars (http://www.scientificamerican.com/article/experts-time-division-days-hours-minutes/). It wasn't until the Greeks around 100BC that we see the hours becoming fixed length (although average people used seasonally varying hours for hundreds of years after this: not until mechanical clocks of the 14th century did this stop). From the 16th century until 1972, though, minutes and seconds were uniform set by the fixed hour. So although sexagesimal notation for time was invented thousands of years ago around the birth of Christ, it wasn't until really good mechanical clocks of the 16th century that one could say that the radix was truly fixed. Which leads me to why I equivocated. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
