[tz] Norfolk Island, Daylight Saving Time (DST) 6/10/19-05/04/20 [SEC=UNCLASSIFIED]

Paul Eggert eggert at cs.ucla.edu
Thu Aug 15 00:26:45 UTC 2019

Brian Inglis wrote:
> As thin as in an Australian winter: that page is not "normative" legislation,
> which by default refers to the local legal time in effect in the reference, as
> stated in 8(1) and 8(2)

Unfortunately the Norfolk Island legislation is ambiguous. By stating that DST 
ends at 2 o'clock, it allows either a 02:00->01:00 transition (which occurs at 2 
o'clock local time, valid legal daylight saving time at the instant of 
transition), or a 03:00->02:00 transition (which also occurs at 2 o'clock local 
time, valid legal standard time at the instant of transition).

This ambiguity is inherent to timestamps near a fallback transition. It's not an 
ambiguity that can occur with tzdb timestamps, since our digital clocks would 
tick from 01:59.999999999 to 01:00 (or from 02:59.999999999 to 02:00) during a 
fallback transition. However, it can occur in the continuous-time model that 
legislation invariably uses.

Possibly the Norfolk Island legislation copied boilerplate from other Australian 
law, in which case the legal wording is ambiguous elsewhere in Australia. It 
would be helpful if the Australians would add a phrase or two to disambiguate 
this, the next time they change their DST laws.

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