{
  "name": "Calendar year vs. reference year lengths",
  "desc": "How much longer the Julian and Gregorian average years are than two reference years for AD 2000, in days and seconds per year, and how many years it takes to build up one day. Reference values are single values quoted from the source, treated as rounded to five decimals.",
  "lic": "CC BY 4.0",
  "lic_url": "https://creativecommons.org/licenses/by/4.0/",
  "by": "The Yardstick Almanac",
  "url": "https://theyardstickalmanac.com/calendars/gregorian-leap-year-rule/",
  "from": [
    "Mean tropical year (AD 2000, 365.24219 days) and vernal equinox year (AD 2000, 365.24237 days): single values quoted from Explanatory Supplement to the Astronomical Almanac, ch. 15, Table 15.1 and sec. 15.1.12",
    "Gregorian and Julian leap-year rules, Explanatory Supplement to the Astronomical Almanac, ch. 15, sec. 15.4.2 and 15.3.5"
  ],
  "how": "Compiled by The Yardstick Almanac from the data listed",
  "data_by": [
    "Computed from the leap-year rules and the AD 2000 year lengths quoted from the Explanatory Supplement to the Astronomical Almanac, ch. 15 (Table 15.1, sec. 15.1.12), 2026-11-01, CC BY 4.0"
  ]
}