
1 
These Regulations may be cited as the Units of Measurement Regulations 2001 and shall come into force on 8th February 2001.
2 
In these Regulations—
 “the Act” means the Weights and Measures Act 1985, and
 “the Regulations” means the Units of Measurement Regulations 1986.
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(1) The Act shall be amended as follows.
(2) In section 8(5A), after the words “the use for trade” there shall be inserted “up to and including 31 December 2009,”.
4 

(1) The Regulations shall be amended as follows.
(2) In regulation 7, after the words “specified circumstances”, there shall be inserted “up to and including 31 December 2009”.
(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:“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”.”.
(4) In paragraph 2 of Schedule 1, the definitions of the SI supplementary units shall be replaced as follows:“
The radian is the angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius.
(International standard ISO 31-1: 1992. British Standard BS 5775-1:1993)
The 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.
(International standard ISO 31-1: 1992. British Standard BS 5775-1:1993).”
(5) Paragraph 4 of Schedule 1 shall be replaced by the following:“
4 


Quantity   
Energy Electronvolt eV The electron volt is the kinetic energy acquired by an electron in passing through a potential difference of 1 volt in vacuum.
Mass Unified atomic mass unit u The unified atomic mass unit is equal to 1/12 of the mass of an atom of the nuclide 12C
Note: The prefixes and their symbols listed in Schedule 2 may be used in conjunction with these two units and with their symbols.”.
(6) In Schedule 2, the table below the heading shall be replaced by the following:“

Factor Prefix Symbol Factor Prefix Symbol
1024 yotta Y 10−1 deci d
10 21 zetta Z 10− 2 centi c
10 18 exa E 10−3 milli m
10 15 peta P 10− 6 micro μ
10 12 tera T 10−9 nano n
109 giga G 10−12 pico p
106 mega M 10−15 femto f
103 kilo k 10− 18 atto a
102 hecto h 10− 21 zepto z
10 1 deca da 10−24 yocto y”
.
Kim Howells
Parliamentary Under-Secretary of State for Consumers and Corporate Affairs,
Department of Trade and Industry
10th January 2001