{
  "name": "Calibration card: Eratosthenes' Earth circumference",
  "desc": "The values in the Calibration card at the top of the page, one field per row, with the source of each value.",
  "lic": "CC BY 4.0",
  "lic_url": "https://creativecommons.org/licenses/by/4.0/",
  "by": "The Yardstick Almanac",
  "url": "https://theyardstickalmanac.com/scale/eratosthenes-earth-circumference/",
  "from": [
    "Pliny, Natural History, Book 2 (chapters 21, 75, 112, 113) and translators' note 261, trans. Bostock and Riley 1855 (Project Gutenberg #57493), public domain",
    "Yard 0.9144 m and inch 25.4 mm, exact equivalents effective July 1, 1959 (24 FR 5348)",
    "WGS 84 ellipsoid a = 6,378,137 m, 1/f = 298.257223563, from PROJ 9.8.1 src/ellps.cpp (MIT; values correspond to NGA TR8350.2)"
  ],
  "how": "Compiled by The Yardstick Almanac from the data listed",
  "data_by": [
    "Pliny, Natural History, trans. Bostock and Riley 1855 (public domain); WGS 84 parameters from PROJ 9.8.1 (MIT); computed 2026-11-01, CC BY 4.0"
  ]
}