{
  "name": "Where ISO week 1 starts, for each weekday of January 1",
  "desc": "One row per weekday on which January 1 can fall: an example year, the Monday that starts ISO week 1, how many early-January days still belong to the previous ISO year, how many late-December days belong to the new week 1, and how many years of the 400-year cycle start on that weekday, with how many of them are leap years and have a week 53.",
  "lic": "CC BY 4.0",
  "lic_url": "https://creativecommons.org/licenses/by/4.0/",
  "by": "The Yardstick Almanac",
  "url": "https://theyardstickalmanac.com/calendars/iso-week-number/",
  "from": [
    "Python 3.15.2 documentation, datetime module: date.isocalendar(), date.fromisocalendar() and the strftime() format codes %G, %V, %u, %W and %U (Python Software Foundation License Version 2; read 2026-11-01)",
    "E. M. Reingold and N. Dershowitz, CALENDRICA 4.0, calendar.l, Section: ISO Calendar, iso-long-year? (Apache License 2.0; read 2026-11-01)"
  ],
  "how": "Compiled by The Yardstick Almanac from the data listed",
  "data_by": [
    "Week rule from the Python datetime documentation and CALENDRICA 4.0 (Apache License 2.0); computed 2026-11-01 with two independent date routines, CC BY 4.0"
  ]
}