BS EN 80000-13:2009 pdf free download – Quantities and units – Part 13: Information science and technology.
Such units are separated from the SI units in the item by use of a broken line between the SI units and the other units.
C) Non-SI units currently accepted by the CIPM for use with the SI are given in small print (smaller than the text size) in the Conversion factors and remarks” column.
d) Non-SI units that are not recommended are given only in annexes in some parts of ISO/lEG 80000. These annexes are informative, in the first place for the conversion factors, and are not integral parts of the standard. These deprecated units are arranged in two groups:
1) units in the CGS system with special names:
2) units based on the foot. pound, second, and some other related units.
e) Other non-SI units given for information, especially regarding the conversion factors, are given in another informative annex.
0.3.2 Remark on units for quantities of dimension one, or dimensionless quantities
The coherent unit for any quantity of dimension one, also called a dimensionless quantity, is the number one, symbol 1. When the value of such a quantity is expressed, the unit symbol 1 is generally not written out explicitly.
Considering that plane angle is generally expressed as the ratio of two lengths and solid angle as the ratio of two areas, in 1995 the CGPM specified that, in the SI, the radian, symbol rad, and steradian, symbol sr, are dimensionless derived units. This implies that the quantities plane angle and solid angle are considered as derived quantities of dimension one. The units radian and steradian are thus equal to one; they may either be omitted, or they may be used in expressions for derived units to facilitate distinction between quantities of different kinds but having the same dimension.
0.4 Numerical statements in this International Standard
The sign = is used to denote Is exactly equal to”, the sign is used to denote is approximately equal to”, and the sign := is used to denote “is by definition equal to”.
Numerical values of physical quantities that have been experimentally determined always have an associated measurement uncertainty. This uncertainty should always be specified. In this standard, the magnitude of the uncertainty is represented as in the following example.
In this example, I , the numerical value of the uncertainty b indicated in parentheses is assumed to apply to the last (and least significant) digits of the numerical value a of the length I. This notation is used when b represents one standard uncertainty (estimated standard deviation) in the last digits of a. The numerical example given above may be interpreted to mean that the best estimate of the numerical value of the length I. when I is expressed in the unit metre. is 2,347 82. and that the unknown value of / is believed to lie between (2.347 82 — 0.000 32) m and (2,347 82 + 0,000 32) m with a probability determined by the standard uncertainty 0.000 32 m and the probability distribution of the values of I.