Branch: Tag:

2016-11-26

2016-11-26 11:37:29 by Henrik Grubbström (Grubba) <grubba@grubba.org>

Updated to tzdata2016j.

8:    Time zone abbreviations    Accuracy of the tz database    Time and date functions +  Interface stability    Calendrical issues    Time and time zones on Mars   
342:    non-hour-based system at night.       * Early clocks were less reliable, and data entries do not represent -  this unreliability. +  clock error.    -  * As for leap seconds, civil time was not based on atomic time before -  1972, and we don't know the history of earth's rotation accurately -  enough to map SI seconds to historical solar time to more than -  about one-hour accuracy. See: Morrison LV, Stephenson FR. +  * The tz database assumes Universal Time (UT) as an origin, even +  though UT is not standardized for older time stamps. In the tz +  database commentary, UT denotes a family of time standards that +  includes Coordinated Universal Time (UTC) along with other variants +  such as UT1 and GMT, with days starting at midnight. Although UT +  equals UTC for modern time stamps, UTC was not defined until 1960, +  so commentary uses the more-general abbreviation UT for time stamps +  that might predate 1960. Since UT, UT1, etc. disagree slightly, +  and since pre-1972 UTC seconds varied in length, interpretation of +  older time stamps can be problematic when subsecond accuracy is +  needed. +  +  * Civil time was not based on atomic time before 1972, and we don't +  know the history of earth's rotation accurately enough to map SI +  seconds to historical solar time to more than about one-hour +  accuracy. See: Morrison LV, Stephenson FR.    Historical values of the Earth's clock error Delta T and the    calculation of eclipses. J Hist Astron. 2004;35:327-36    <http://adsabs.harvard.edu/full/2004JHA....35..327M>;
601:       * The format of the country code file, documented in iso3166.tab.    - When these interfaces are changed, an effort is made to preserve - backward compatibility. For example, tz data files typically do not - rely on recently-added zic features, so that users can run older zic - versions to process newer data files. +  * The version number of the code and data, as the first line of +  the text file 'version' in each release.    -  + Interface changes in a release attempt to preserve compatibility with + recent releases. For example, tz data files typically do not rely on + recently-added zic features, so that users can run older zic versions + to process newer data files. The tz-link.htm file describes how + releases are tagged and distributed. +    Interfaces not listed above are less stable. For example, users   should not rely on particular UT offsets or abbreviations for time   stamps, as data entries are often based on guesswork and these guesses