{
  "name": "Drift against a fixed year, 1600–2400",
  "desc": "Calendar days elapsed since January 1, 1600, minus 365.24219 days times the years elapsed, at January 1 of each year, under the Julian and Gregorian rules. The reference year is held fixed for illustration.",
  "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": [
    "Gregorian and Julian leap-year rules, Explanatory Supplement to the Astronomical Almanac, ch. 15, sec. 15.4.2 and 15.3.5",
    "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"
  ],
  "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"
  ]
}