{
  "url": "https://openlegislation.uk/units-of-measurement-regulations-2001/regulation-4",
  "json_url": "https://openlegislation.uk/units-of-measurement-regulations-2001/regulation-4.json",
  "legislation": "uksi/2001/55",
  "legislation_title": "The Units of Measurement Regulations 2001",
  "legislation_url": "https://openlegislation.uk/units-of-measurement-regulations-2001",
  "path": "regulation/4",
  "kind": "regulation",
  "number": "4",
  "heading": "Amendment of the Regulations",
  "text": "(1) The Regulations shall be amended as follows.\n(2) In regulation 7, after the words “specified circumstances”, there shall be inserted “up to and including 31 December 2009”.\n(3) In paragraph 1 of Schedule 1, the text under the table which appears beneath the heading “Special name and symbol of the SI unit of temperature for expressing Celsius temperature.” shall be replaced as follows:\n“Celsius temperature t is defined as the difference t = T − To between the two thermodynamic temperatures T and To where To = 273, 15 K. An interval or difference of temperature may be expressed either in kelvins or in degrees Celsius. The unit “degree Celsius” is equal to the unit “kelvin”.”.\n(4) In paragraph 2 of Schedule 1, the definitions of the SI supplementary units shall be replaced as follows:\n“Unit of plane angle\nThe radian is the angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius.\n(International standard ISO 31-1: 1992. British Standard BS 5775-1:1993)\nUnit of solid angle\nThe steradian is the solid angle of a cone which, having its vertex in the centre of a sphere, cuts off on the surface of the sphere an area equal to that of a square with sides of length equal to the radius of the sphere.\n(International standard ISO 31-1: 1992. British Standard BS 5775-1:1993).”\n(5) Paragraph 4 of Schedule 1 shall be replaced by the following:\n“Units used with the SI, whose values in SI are obtained experimentally\n4 Quantity\nNote: The prefixes and their symbols listed in Schedule 2 may be used in conjunction with these two units and with their symbols.\nEnergy\nElectronvolt\neV\nThe electron volt is the kinetic energy acquired by an electron in passing through a potential difference of 1 volt in vacuum.\nMass\nUnified atomic mass unit\nu\nThe unified atomic mass unit is equal to 1/12 of the mass of an atom of the nuclide 12C\n”.\n(6) In Schedule 2, the table below the heading shall be replaced by the following:\n“\nFactor\nPrefix\nSymbol\nFactor\nPrefix\nSymbol\n1024\nyotta\nY\n10−1\ndeci\nd\n10 21\nzetta\nZ\n10− 2\ncenti\nc\n10 18\nexa\nE\n10−3\nmilli\nm\n10 15\npeta\nP\n10− 6\nmicro\nμ\n10 12\ntera\nT\n10−9\nnano\nn\n109\ngiga\nG\n10−12\npico\np\n106\nmega\nM\n10−15\nfemto\nf\n103\nkilo\nk\n10− 18\natto\na\n102\nhecto\nh\n10− 21\nzepto\nz\n10 1\ndeca\nda\n10−24\nyocto\ny\n”\n.",
  "extent": null,
  "status": null,
  "version": "current",
  "annotations": [],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/uksi/2001/55/regulation/4",
    "retrieved_at": "2026-10-29T08:07:27.619160+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}