# ISO 17-1973

Disclosure to Promote the Right To InformationWhereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. इंटरनेट मानक“!ान $ एक न’ भारत का +नम-ण”Satyanarayan Gangaram Pitroda“Invent a New India Using Knowledge”“प0रा1 को छोड न’ 5 तरफ”Jawaharlal Nehru“Step Out From the Old to the New”“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan“The Right to Information, The Right to Live”“!ान एक ऐसा खजाना जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam“Knowledge is such a treasure which cannot be stolen”ैIS 1076-2 (1985): Preferred Numbers, Part 2: Guide to theUse of Preferred Numbers and Series of Preferred Numbers[PGD 1: Basic Standards]IS: 1076 (Part 2) -1985 UDC 389’171 ( 026 ) IS0 17 - 1973 Indian Standard PREFERRED NUMBERS PART 2 GUIDE TO THE USE OF PREFERRED NUMBERS AND SERIES OF PREFERRED NUMBERS ( Second Revision ) Uational Foreword This Indian Standard ( Part 2) (Second Revision ) is identical with IS0 17 - 1973 ‘Guide to :he use of preferred numbers and series of preferred numbers’ issued by the International Organiza- ion for Standardization ( IS0 ), was adopted by the Indian Standards Institution on the recommen- fation of Engineering Standards Sectional Committee and approval of the Mechanical Engineering Xvision Council. Originally published in 1957, this standard was intended: a) to give authoritative status to preferred numbers for application where appropriate, b) to provide readily accessible information on ‘the numbers themselves for those who have occasion to use them, and c) to give guidance to the use of preferred numbers ( and of series of preferred number ). The main object of first revision of the standard in 1967 was to give guidance in the use of more rounded valves and to set out the danbers and disadvantages of using them as compared with the advantages of using preferred numbers themselves. In the present revision, the standard has been split up in parts to bring it in line -with IS0 standards, by adoption of the relevant IS0 standard. In the adopted standard certain terminology and convention are not identical with those used in Indian Standards; attention is specially drawn to the following: Comma ( , ) has been used as a decimal marker while in Indian Standards the current practice is to use point ( . ) as the decimal marker. Wherever the words ‘International Standard’ appear referring to this standard, they should be read as ‘Indian Standard’. Additional Information. .This Indian Standard is issued in several parts, each part being identical w.ith a corresponding IS0 standard indicated within brackets. IS : 1.076 Preferred numbers: Part 1 Series of preferred numbers ( IS0 3 ). Part 2 Guide to the use of preferred numbers and of series of preferred numbers ( IS0 17 ). Part 3 Guide to the choice-of series of preferred numbers and of series containing more rounded valuesof preferred numbers ( IS0 497 ). Adopted 30 July 1986 I (Q December 1987, BIS Or 3 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH 2AFAR MARG NEW DELHI tlOOO2 IS: 1076 ( Part-2) -1985 IS0 17 - 1973 Preferred numbers were first utilized in France at the end -of the nineteenth century. From 1877 to 1879, Captain Charles Renard, an officer in the engineer corps, made a rational study of the elements necessary in the construction of lighter-than-air aircraft. He computed the specifications for cotton rope according to a grading system, such that this element could be produced in advance without prejudice to the installations where such rope was subsequently to be utilized. Recognizing the advantage to be derived from the geometrical progression, he adopted, as a basis, a rope having-a mass of a grams per metre, and as a grading system, a rule that would yield a tenth multiple of the value a after every fifth step of the series, i.e. : aX95=lOa or 9=vlO whence the following numerical series : a a710 a( 710)’ a(q10j3 a (q10j4 1Oa the values of which, to 5 significant figures, are : a 1,5849a 2,5119a 3,981l a 6.3096a 10a Renard’s theory was to substitute, for the above values, more rounded but more practical values, and he adopted asa a power of 10, positive, nil or negative. He thus obtained the following series : 10 16 25 40 63 100 which may be continued in both directions From this series, designated by the symbol R 5, the R 10, R 20, R 40 series were formed, each adopted ratio being the square root of the preceding one : ‘V/10 2vlo aTI0 The first standardization drafts were drawn up on these bases in Germany by the Normenausschuss der Deutschen lndustrie on 13 April 1920, and in France by the Commission permanente de standardisation in document X of 19 December 1921. These two documents offering few differences, the commission of standardization in the Netherlands proposed their unification. An agreement was reached in 1931 and, in June 1932, the International Federation of the National Standardizing Associations organized an international meeting in Milan, where the ISA Technical Committee 32, Preferrednumbers, was set up and its Secretariat assigned to France. On 19 September 1934, the ISA Technical Committee 32 held a meeting in Stockholm; sixteen nations were represented : Austria, Belgium, Czechosiovakia, Denmark, Finland, France, Germany, Hungary, Italy, Netherlands, Norway, Poland, Spain, Sweden, Switzerland, U.S.S.R. . 4 With the exception of the Spanish, Hungarian and Italian delegations which,~although favourable, had not thought fit-to give their final agreement, all the other delegations accepted the draft which was presented. Furthermore, Japan communicated by letter its approval of the draft as already discussed in Milan. As a consequence of this, the international recommendation was laid down in ISA Bulletin 11 (December 1935). After the Second World War, the work was resumed by ISO. The Technical Committee ISO/TC 19, Preferred numbers, hx set up and France again held the Secretariat. This Committee at its first meeting, -which took place in Paris in July 1949, recommended the adoption by IS0 of the series of preferred numbers defined by the table of ISA Bulletin 11, i.e. R 5, R IO, R 20, R 40. This meetirrg was attended by representatives of the 19 following nations : Austria, Belgium, Czechoslovakia, Denmark, Finland, France, Hungary, India, Israel, Italy, Netherlands, Norway, Poland, Portugal, Sweden, Switzerland, United Kingdom, U.S.A., U.S.S.R. During the subsequent meetings in New York in 1952 and in the Hague in 1953, whichwere attended also by Germany, the series R 80 was added and slight alterations were made. The draft thus amended became IS0 Recommendation R 3. 2 1 SCOPE AND FIELD OF APPLICATION This International Standard constitutes a guide to the use of-preferred numbers and of series of preferred numbers. 2 REFE,RENCES ’ IS0 3, Preferred numbers - Series of preferred numbers. ,,’ Is0 497, Guide to the choice of series of preferred numbers and of series containing more rounded values of preferred numbers. 3 GEOMETRICAL~PROGRESSIDNS AND PREFERRED NUMBERS 3.1 Standard series of numbers In all the fields where a scale of numbers is necessary, standardization consists primarily of grading the characteristics according to one or several series of numbers covering all the requirements with a minimum df ternls. These series should present certain essential charadteristics; they shoutd a) be simple and easily remembered; b) be unlimited, both towards the lower and towards the higher numbers; c) include all the decimal multiples and/sub-multiples of any term; d) provide a rational grading system. 3.2 Characteristics of geometrical progressions which include the number 1 The characteristics of these progressions, with a ratio 9, are mentioned below. 39.1 The product or quotient of any two terms 9* and 9c of such a progression is always a term of that progression : qb X qz = qb+c 3.22 The integral positive or negative power c of any term 9* of such a progression is always a term of that progression : (9b)~ = 9bc IS:1076(Part2)-1985 BSO 77 - 1973 3.2.3 The fractional positive or negative power l/c of a term 96 of such a progression is still a term of that progression, provided that b/c be an integer : tqb)l /c = 9b/c 3.2.4 The sum or difference of two. terms of such a progression is not generally equal to a term of that progression. However, there exists one geometrical progression such that one of its terms is equal to the sum of the two preceding terms. Its ratio 1 +J5 2 approximaies 1,6 (it is the Go/den Section of the Ancients). i 3.3 Geometrical progressions which include the number 1 and the ratio of which is a root of 10 The progressions chosen to compute the preferred numbers have a ratio equal to q/10, r being equal to 5,‘to 10, to 20, or to 40. The results are given hereunder. 3.3.1 The number 10 and its positive and negative powers are terms of all the progressions. 3.3.2 Any term whatever of the range 10d . lOd+l. d being positive or negative, ~may be obtained~by multiplying by lad the corresponding term of the range 1 . . . 10. 3.3.3 The terms of these progressions comply in particular with the property given in 3.1 c). 3.4 Rounded off geometrical progressions The preferred numbers are the rounded off values of the progressions defined in 3.3. 3.4.1 The maximum roundings off are : -t 1,26% and - 1,Ol % The preferred numbers included in the range 1 . . . 10 are given in the table of section 2 of IS0 3. 3.4.2 Due to the rounding off, the products, quotients and powers of preferred numbers may be considered as preferred numkrs only if the modes of calculation referred to in section 5 are used. 3 IS: 1076 (Part 2) -1985 IS0 17 - 1973 3.4.3 For the R 10 series, it should be noted that’310 is equal to 32 at an accuracy closer than 1 in 1 000 in relative value, so that - the cube of a number of this series is approximately equal to double the cube of the preceding number. In other words, the Nth term is approximately double the (N - 31th term. Due to the rounding off,~it is found that it is usually equal to exactly the double; - the square of a number of this series is approximately equal to 1.6 times the square of the preceding number. 3.4.4 Just as the terms of the R 10 series are doubled in general every 3 terms, the terms of the R 20 series are doubled every 6 terms, and those of the R 40 series are doubled every 12 terms. 3.4.5 Beginning with the R 10 series, the number 3,15, which is nearly equal to TI, can be found among the preferred numbers. It follows that the length of a circumference and the area of a circle, the diameter of which is a preferred number, may also be expressed by preferred numbers. This applies in particular to peripheral speeds, cutting speeds, cylindrical areas and volumes, spherical areas and volumes. 3.4.6 The R 40 series of preferred numbers includes the numbers 3 000, 1 500, 750, 375, which have special importance in electricity (number of revolutions per minute of asynchronous motors when running without load on alternating current at 50 Hz). 3.4.7 It follows from the features outlined above that the preferred numbers correspond faithfully to the characteristics set forth in 3.1. Furthermore, they constitute a unique grading rule, acquiring thus a remarkably universal character. 4 DIRECTIVES FOR THE USE OF PREFERRED NUMBERS 4.1 Characteristics expressed by numerical values In the preparation of a project involving numerical values of characteristics, whatever their nature, for which no particular standard exists, select preferred numbers for these values and do not deviate from them except for imperative reasons (see section 7). Attempt at all times to adapt existing standards to preferred numbers. 4.2 Scale of numerical values In selecting a scale of numerical values, choose that series having the highest ratio consistent with the desiderata to be satisfied, in the order : R 5, R 10, etc. Such a scale must be carefully worked out. The considerations to be taken into account are, among others : the use that is to be made of the articles standardized, their cost price, their dependence upon other articles used in close connection with them, etc. The best scale will be determined by taking into consideration, in particular, the two following contradictory tendencies : a scale with too wide steps involves a waste of materials and an increase in the cost of manufacture, whereas a too closely spaced scale leads to an increase in the cost of tooling and also in the value of stock inventories. When the needs are not of the same relative importance in all the ranges under consideration, select the most suitable basic series for each range so that the sequences of numerical values adopted provide a succession of series of different ratios permitting new interpolationswhere necessary. 4.3 Derived series Derived series, which are obtained by taking the terms at every second, every third, every fourth, etc. step of the basic series, shall be used only when none of the scales of the basic series is satisfactory. 4.4 Shifted series A shifted series, that is, a series having the same grading as a basic series, but beginning with a term not belonging to that series, shall be used only for characteristics which are functions of other characteristics, themselves scaled in a basic series. Example : The R 80/8 (25.8 . . 165) series has the same grading as the R 10 series, but starts with a term of the R 80 series, whereas the R 10 series, from which it is shifted, would start at 25. 4.5 Single numerical value In the selection of a single numerical value, irrespective of any idea of scaling, choose one of the terms of the R 5, R 10, R 20, R 40 basic series or else a term of the exceptional R 80 series, giving preference to the terms of the series of highest step ratio, choosing R 5 rather than R 10, R 10 rather than R 20, etc. When it is not possible to provide preferred numbers for all characteristics that could be numerically expressed, apply preferred numbers first to the most important characteristic or characteristics, than determine the secondary or subordinate characteristics in the light of the principles set forth in this section. 4.6 Grading by means of preferred numbers The preferred numbers may differ from the calculated values by -!- 1,26 % to - 1 ,Ol %. It follows that sizes, graded according to preferred numbers, are not exactly proportional to one another. To obtain an exact proportionalit