The Units of Measurement Regulations 2001

Amendment of the Regulations

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 − T_o between the two thermodynamic temperatures T and T_o where T_o = 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:

“Unit of plane angle

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)

Unit of solid angle

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:

“Units used with the SI, whose values in SI are obtained experimentally

4.  

Quantity
Note: The prefixes and their symbols listed in Schedule 2 may be used in conjunction with these two units and with their symbols.”.
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

(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”

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