Fwd: Question about time period transition points
Wise ones of the TZ list, A (quite academic, but possibly interesting) question came up here as we're trying to document the behaviour of our time zone code. We're trying to figure out whether the transition time is reached or skipped. For example, for these 2 rules, # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule TC 1979 1986 - Apr lastSun 2:00 1:00 D Rule TC 1979 2006 - Oct lastSun 2:00 0 S does the clock reach "2:00" on the transition days? In that case, the transition would go from "2:00(S)" -> "3:00(D) + epsilon" when moving forward, and "2:00(D)" -> "1:00(S) + epsilon" when moving back. Or does it go from "2:00(S) - epsilon" -> "3:00(D)" and "2:00(D) - epsilon" -> "1:00(S)" ? If the transition time IS reached, which "name" would attach to it? Phrased differently, for the Americas/NewYork transitions this spring: 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00 AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March") 2) Is the designation of that coordinate (in the local New York City timezone) "EDT" or "EST"? Thanks! Mike
Phrased differently, for the Americas/NewYork transitions this spring: 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00 AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
2) Is the designation of that coordinate (in the local New York City timezone) "EDT" or "EST"?
At least in the United States, time transitions from 1:59:59 AM EST to 3:00:00 AM EDT. I don't know if other countries have different rules, but it would be surprising to me if they did. - Adam
On Feb 14, 2011, at 2:39 PM, Adam Vartanian wrote:
Phrased differently, for the Americas/NewYork transitions this spring: 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00 AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
2) Is the designation of that coordinate (in the local New York City timezone) "EDT" or "EST"?
At least in the United States, time transitions from 1:59:59 AM EST to 3:00:00 AM EDT. I don't know if other countries have different rules, but it would be surprising to me if they did.
The changeover time is just as much an arbitrary political decision as all the other aspects of DST change. So yes, you can find a variety of changeover times. You can find them in the "AT" column in the rules files. paul
On Mon, Feb 14, 2011 at 2:44 PM, Paul Koning <paul_koning@dell.com> wrote:
On Feb 14, 2011, at 2:39 PM, Adam Vartanian wrote:
Phrased differently, for the Americas/NewYork transitions this spring: 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00 AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
2) Is the designation of that coordinate (in the local New York City timezone) "EDT" or "EST"?
At least in the United States, time transitions from 1:59:59 AM EST to 3:00:00 AM EDT. I don't know if other countries have different rules, but it would be surprising to me if they did.
The changeover time is just as much an arbitrary political decision as all the other aspects of DST change. So yes, you can find a variety of changeover times. You can find them in the "AT" column in the rules files.
Paul, That makes sense. However, combining your answer and Adam's, it looks like the "AT" time isn't actually reached? The current "northamerica" file shows an AT time of 2:00, not 1:59:59. Am I misreading it? Thanks, Mike
On Feb 14, 2011, at 2:53 PM, Mike Giroux wrote:
On Mon, Feb 14, 2011 at 2:44 PM, Paul Koning <paul_koning@dell.com> wrote:
On Feb 14, 2011, at 2:39 PM, Adam Vartanian wrote:
Phrased differently, for the Americas/NewYork transitions this spring: 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00 AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
2) Is the designation of that coordinate (in the local New York City timezone) "EDT" or "EST"?
At least in the United States, time transitions from 1:59:59 AM EST to 3:00:00 AM EDT. I don't know if other countries have different rules, but it would be surprising to me if they did.
The changeover time is just as much an arbitrary political decision as all the other aspects of DST change. So yes, you can find a variety of changeover times. You can find them in the "AT" column in the rules files.
Paul,
That makes sense. However, combining your answer and Adam's, it looks like the "AT" time isn't actually reached?
The current "northamerica" file shows an AT time of 2:00, not 1:59:59.
Am I misreading it?
No. It means at 2:00:00.00000000, so indeed you don't get to see that time because it becomes 3:00:00.000000 DST instead. paul
At least in the United States, time transitions from 1:59:59 AM EST to 3:00:00 AM EDT. I don't know if other countries have different rules, but it would be surprising to me if they did.
The changeover time is just as much an arbitrary political decision as all the other aspects of DST change. So yes, you can find a variety of changeover times. You can find them in the "AT" column in the rules files.
Changeover times obviously vary, but I'd be surprised if anyone set up their rule such that the time change happened immediately after the changeover time rather than at the changeover time (eg, at exactly one second after 3:59:59 it was 4:00:00, but one second plus epsilon after 3:59:59 it was 5:00:00). In practical terms, it wouldn't actually make any difference, but I would find it surprising if anyone's rules were written that way. - Adam
participants (3)
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Adam Vartanian -
Mike Giroux -
Paul Koning