[tz] Fwd: Re: [english 83%] Re: historic Oslo times
apb at cequrux.com
Wed Mar 11 06:47:17 UTC 2015
On Tue, 10 Mar 2015, Meno Hochschild wrote:
> Okay, now I have done my own investigations and found following
> If the switch (expressed as UNTIL-time in a ZONE-line) is before
> any dst-rule valid for given UNTIL-related year then we have to
> apply the previous daylight saving offset valid at that time
> (previous means before the switch).
That sounds like one of the consequences of the way Zones and
My explanation would be more like this:
The lines associated with a "Rule" define the instants of
transition between standard time and DST, and the offset
associated with each transition. These transitions are uses by
all Zones that follow the Rule.
A line associated with a "Zone" may refer to a particular Rule,
along with the instant at which the zone starts following the
Rule, the instant at which the Zone ceases following the Rule, and
the standard time offset from UTC during the interval between the
start and end time. For all times within the interval that the
Zone follows the Rule, the DST offsets and DST transitions defined
by the Rule apply to the Zone.
The Zone might or might not incur a standard time transition
and/or a DST transition at the instant when the zone begins or
ceases to follow the Rule. To figure out whether or not there are
standard time transitions or DST transitions at these instants,
one needs to determine both the standard time offset from UTC, and
the DST offset from standard time, at the instants just before and
just after the Zone begins to follow the Rule, or ceases to follow
the Rule; any differences in the offsets imply that there is a
transition at that instant.
--apb (Alan Barrett)
More information about the tz