[LEAPSECS] What's the point?

Warner Losh imp at bsdimp.com
Wed Feb 9 11:49:32 EST 2011

On 02/09/2011 09:05, Rob Seaman wrote:

> Tony Finch wrote:


>> Warner Losh wrote:


>>> Rob Seaman wrote:


>>>> C) As pointed out on numerous occasions in the past, these kaleidoscopic timezones would accelerate quadratically just like leap seconds.

>>> This problem isn't solved by this method either. True.

>> Except that timezone adjustments continue to work much further into the future than leap seconds.

> No - the 2nd derivative is the same whether the leap-second-equivalents (LSEs) are batched one-by-one or 3600 at a time. (Putting aside the question of whether timezone adjustments would meet the project requirements in the first place.)

It is a lot easier to adjust by an hour for local time than it is to
have a leap second every month, or more often. Thus Tony is right: the
zoneinfo files adjusting local time via timezone shifts mandated by
local government would easily outlast leap seconds.

To be clear also: the idea isn't to adjust the TI time to local sun time
frequently, but only when it drifts by an hour or so. That's why I keep
saying that timezone changes would be on the order of a few dozen every
few hundred years. This is in the noise compared to the recent timezone
changes which happen on the order of dozens per year.

> The current leap second policies are constrained to twice per year - this would correspond to a timezone do-se-do of 1800 years. The actual standard, though, is 12 per year - that brings it down to 300 years, which seems similar in level of intrusiveness. Larger interruptions must occur less frequently to be tolerated.

I'm not sure I follow this point...

> However, a leap second per day (or even multiples) is not logistically out of the question. This is Mark Calabretta's epsilon. One-per-day would mean a timezone reorganization every ten years, which would be absurdly unacceptable compared to taking our daily epsilon vitamin.

The US changes its timezone rules on average every 10 years (DST has
been uniform for 45 years or so and has changed 5 times). Tweaks to the
US timezone rules happen annually for different parts of the country
(this country moves from this timezone to that, etc).

> Leap seconds would be much more robustly tolerated into the far distant future than rubber timezones.

what are rubber timezones that you talk about? I don't think we're
talking about the same thing.

The idea that's been put forth is that the transition would be made all
at once. Eastern Time zone would go from TI-5 to TI-4, most likely by
failing to fallback one year in the fall.


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