{
  "name": "Three mass differences around the kilogram prototype",
  "desc": "One row per claim: the 1889 limit for national prototypes, the median difference found in 1989–1991, and the prototype's uncertainty from 2019, in micrograms and relative to 1 kg.",
  "lic": "CC BY 4.0",
  "lic_url": "https://creativecommons.org/licenses/by/4.0/",
  "by": "The Yardstick Almanac",
  "url": "https://theyardstickalmanac.com/units/kilogram-definition/",
  "from": [
    "BIPM, The International System of Units (SI), 9th edition, version 4.01 (June 2026), CC BY 4.0",
    "CGPM, 26th meeting (2018), Resolution 1, On the revision of the International System of Units (SI), in force from 20 May 2019"
  ],
  "how": "Compiled by The Yardstick Almanac from the data listed",
  "data_by": [
    "SI Brochure, 9th edition, version 4.01, Appendices 1 and 4, and CGPM Resolution 1 (2018), by the BIPM, CC BY 4.0 (adapted: converted to micrograms); 2026-11-01"
  ]
}