# ISO 497-1973

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 1076-3 (1985): Preferred Numbers, Part 3: Guide to theChoice of Series of Preferred Numbers and of SeriesContaining More Rounded Values of Preferred Number [PGD 1:Basic Standards]z . : C i 0 . . : . i : ; 7 1s :1076(Part3) -1985 , IS0 497 - 1973 hdian Standard PREFERRED NUMBERS PART 3 GUIDE TO THE CHOICE OF SERIES OF PREFERRED NUMBERS AND OF SERIES CONTAINLNG MO-RE ROUNDED VALUES OF PREFERRED NUMBERS ( Second Revision ) National Foreword This Indian Standard ( Part 3 ) ( Second Revision ) which is identical with IS0 497-1973 ‘Guide to the choice of series of preferred numbers and of series containing more rounded values of preferred numbers’ issued by the International Organization for Standardization ( IS0 ) was adopted by the Indian Standards Institution o-n the recommendation of the Engineering Standards Sectional Committee and approved by the Mechanical Engineering Division Council. This standard IS : 1076 was originally published in 1957 and was intended: a) to give authoritative status to preferred numbers for application where appropriate, b) to provide readily accessible information on the number 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 numbers ). The standard was subsequently revised in 1967. The main object of first revision was to give guidance in the use of more rounded values and to set out the dangers and disadvantages of using them as compared with the advantages of using preferred numbers themselves. Second revision of the standard has been made to harmonize it with relevant fwstandard and brought out in parts in line with IS0 Standards. In the adopted standard certain terminology and conventions are not identical with those used in Indian Standards; attention is specially drawn to the following: Comma (,) has been used as decimal marker while in Indian Standards the current practice is to use full point (,) as the decimal marker. Wherever the words ‘International Standard’ appear, referring tothis standard, they should be read as ‘Indian Standard’. Cross Reference international Standard IS0 3-1973 IS0 17-l 973 Additional Information Corresponding Indian Standard IS : 1076 ( Part 1 )-1985 Preferred numbers: Part 1 Series of preferred numbers ( Identical ) IS : 1076 ( Part 2 )-I985 Preferred numbers: Part 2 Guide to the use of preferred numbers and of series of *preferred numbers ( Identical ) This Indian Standard includes a number of parts, each identical with corresponding tSO_standards, indicated within parenthesis: Part 1 ( IS0 3 ) Series of preferred numbers Part2 ( ISO 17 )_ Guide to the use of preferred numbers and of series of preferred numbers Part 3 ( lS0 497 ) Guide to the-choice of series of preferred numbers arid’ of series contain- ing more rounded values of preferred numbers. Adopted 30 July 1985 I 8 March 1987, I!3 Gr 6 . --. - . . -. A . . INDIAN STANDARDS INS1 I I u I IUN MANAK BHAVAN, 9 ‘BAHADUR SHAH ZAFAR MARG NEW DELHI 11,0002 IS : 1076 ( Part 3 ) - 1985 IS0 497 - 1973 1 SCOPE AND FlELD OF APPLICATION This International Standard completes IS0 17 by supplementarv directives regarding the choice of series and the possible tise of more rounded values as mentioned in section 7 of that International Standard : a) it gives the only more rounded values admissible, in the form of two series rounded to a greater or lesser degree; b) it states the conditions on which these more rounded values may be used and the consequences of usingthem; cl It gives rules by means of which any uncertainty In the choice betvueen the pt-eferred numbers and the various more rounded values can be dvoided. 2 REFERENCES IS0 3, Preferred numbers Series of preferred numbers. IS0 17, Guidfx to the IISC? of prcft?rrc~d numben: atd of serit,s of preferred ttutnbtx. 3 ADVANTAGES OF ADHERING STRICTLY TO PREFERRED NUMBEM The advantages of using preferred numbers, set out in IS0 3 and IS0 17, are recalled and amplifted below. These advantages are obtained net merely ~II the standardization of various machine elements by themselves, but above all in th(! construct ion of complete machines when the fu,nctional characteristics, as well as the sizes of each of the various elements, are in a geometricai progression. 3.1 Best progression Preferred numbers ensure the best progression from the point of view of regularity and the possibility of adapting them to new requirements for the creation of closer series by the insertion of intermediate values. 3.2 Universal applicability Preferred numbers offer the most logical means of uninterrupted coverage of the complete range of requirements in a given field (powers of motors, output of pumps, etc.). 3.3 Simplification of technical and commercial calculations Since the products and quotients of preferred numbers are by definition also preferred numbers, calculations, which should be made by using the logarithmic values or serial numbers and not the preferred numbers themselves, al-e considerably simplified, especially when-the series of values (dimensions, list prices, etc.) are multiplied or divided in the same proportions 3.4 Conversion into other svstems of measurement . Convrrsion into other systems- of measurement is greatly facilitated when the series of values in which the measurements at-e PX~I csstd compl use preferred numbers .Ind, iIt the same time, the convv~~io~i f,rctors approximate to prrttl rt~l n~lmbcrs. 2 IS : 1076 (Part 3’)~1985 IS0 497 -1973 4 EXCEPTIONAL USE OF MORE ROUNDED VALUES 4.1 In certain applicaticns, imperative reasons prohibit the cm of the preferred numbers themselves : a) because it is impossible or absurd to retain alt the significant figures, in particular when a whole number is necessary (for example 32 instead of 31,5 for the number of teeth in a gear); b) because, in the absence of any indication of tolerances, the number of significant figures gives the impression of a precision which is neither desired nor measurable (for example l/30 instead of l/31,5 second for time exposures for cameras or 224 for an output which in practice is verified at about 10 %). 4.2 Further, during the t:ansition period, it is possible that preferred numbers may not be accepted by certain branches of Industry or by the qeneral public. for reasons : a) of an economic nature (for example the wish to continue using existing tools and gauges in the factories); b) ot a psychological nature (tor example the wish to use values expressed in a more simple manner, especially when, in a given case, it may be difficult to write or say the number of figures contained in the preferred numbers themselves) .I ) 4.3 The use of more rounded values may therefore be justified by imperative reasons (see 4.1), and these values should thus be used rather than dispensing altogether with the use of preferred numbers. On the other hand, the use of more rounded values should not be permitted for economic or- psychological reasons (see 4.2); since these are subjective reasons and may not be the same everywhere, they could give rise to differing company or national standards, making wider national or international unification difficult.2) 1) Also. in Certain cases where it is useful to have terms with additive properties, the use. awhtcn should remain excepttonal, of more rounded va1ues. such as those of the R” series, provide; a Solution to the problem, to a limited extent at ieast, for example 3 +4 =7 3+5=8 3+6=9 3+7:=10 3.5 t 4,5 = 8 7+7=14 etc. 2) The use of exceptional values which are neither preferred numbers nor more rounded values --whether foi the sake of alignment with existing standards which were not formulated in accordance with preferred numbers and have not yet been revised, or to maintain particular production processes for the sake cf interchangeabi!ity, or to u$e existing tools and gauges - renders future standardization difficult both in the national and international fields and prevents the building of mechines in series with geometrical scaiing. As most IS0 publications are based on preferred numbers, previously established national standards also using them will automatically correspond, but it will be more difficult to align those which include the more rounded values or values which are not related to preferred numbers. Ihe introduction into standards of existing series of values which cannot be modified, such as physical constants, should not be regarded as an application of preferred numbers, even if these valueS are near to preferred numbers or more rounded values; these series may not possess all the propertles of preferred numbers, and their use may create difficulties, particularly in calculdtions WC t, LID those envisaged in 3.4. The same applies t3 existing series of values which it is difficult to modify at present, such as gear modules. As in the Original Standard, this Page is Intentionally Left BlankAs in the Original Standard, this Page is Intentionally Left BlankIS : 1076 (Part 3 ) - 1985 IS0 497 - 1973 6 DANGERS OF USING MORE ROUNDED VALUES 6.1 The presence in a series of a single more rounded value or of an exceptional value admitted by departing from the rule, and which will not be a preferred number, may make it impossible to transfer subsequently to a series with a smaller ratio. 6.2 The scaling of series of more rounded values is not as good as that of preferred numbers series since, for some intervals, the irregularity may reach 2.94 % in the R’ series and even 5.61 % in the R” series (see values at the foot of columns in the tablet )). between 1,32 and 1,7 reaches 1,26 % + 2.51 96 = 3,77 % while the maximum irregularity of the original R’ 40 series is only 2,94 %; the fundamental principle of the regularity of preferred numbers series is thus destroyed. 6.4 The degree of precision of more rounded values is not as great as that of preferred numbers. In fact, this lack of precision may reach 2,51 % for the values in the R’ series and 5,36 % for those of the R” series. Further, because of this fact, more rounded values cannot be used for technical projects when calcu!ating (see section 5 of IS0 17) with the aid of the serial numbers given in column 5 of the table.1 ) 6.3 The scaling of derived series may be even poorer than 6.5 Nat ional and international collaboration in that of the corresponding R’ or R” series, if two adjacent standardization work is rendered much more difficult if, values have been rounded towards each other, for example instead of using preferred numbers, different people choose one downwards and the other upwards; thus, for example different series of rounded values for the solution of the for the R’ 40/4 series (. . 1,05 . . .) the irregularity same problem.2) 1) For example a difference of 5 % on the linear dimension entails a diffetence of more than 10 % on the square lcross section and, consequently, strength of a bolt: cross section of a piston and, consequently, power of a motor), of more than 15 % on the cube (mass of part, bending of a shaft), of more than 20 % on the 4th power (rigidity of a spring], of more than 25 % on the 5th power (moment of inertia) 2) See foow ,te 2) on page 2. 7 OS :1076(Part 3).1985 IS0 497 - 1973 ANNEX PRECISION OF THE VALUES AND REGULARITY OF THE RATIO A.1 DEFINITION In order to understand the disadvantages and dangers of using the more rounded values and to adopt them only with full knowledge of the facts, it is important first of all to consider what may be called the degree of precision in relation to the corresponding theoretical value - of the calculated values, - of the preferred numbers, - of the more rounded values, and the degree of regularity of the ratio of the corresponding series. A.1 .I The degree of precision of a term,’ ’ in relation to the corresponding theoretical value, is characterized by the relationship, expressed as a percentage, - of the difference between the value in question and the theoretical value, -. to this theoretical value. These relative differences are given for the preferred numbers in column 8 of the table in is0 3 and are repeated in this International Standard in column 7 of the table. This table also gives the corresponding differences for the more roundedvalues in columns 8 to 10 A.1.2 The degree of regularity of the ratio of a series, at a given point, is characterized by the deviation, expressed as a percentage, between the actual ratio at this point (relation between two adjacent terms) and the theoretical ratio.*) These deviations, and therefore the degree of regularity of the ratio between two adjacent terms, can thus be obtained by r,imple algebraic subtraction of the differences given in columns 7 to 10 OF the table, ignoring infinitesimal values.3) The maximum irregularity of the ratio at various points rn each of the R, R’ and R” series is given at the foot of columns 1 to 4 of the tabte. A.2 PERMISSIBLE DEVIATIONS A.2.1 If consideration is given only to the condition that a rounded value shall remain closer to the corresponding theoretical value than to the adjacent theoretical values, this condition is expressed by a maximum permissible devration which (if the ratio 30 is not too greatj is approxirnately equal in relative value to p-1 __- 2 A.2.2 At the limit, hovvever, the relation between two successive numbers may thus become near to 1 (or twice the ratio), which is not permissible forthe regularity of the series. A.3 ACTUAL DEVIATIONS OF THE CALCULATED ‘VALUES In IS0 3, the calculated values are given in column 7 of the table to five significant figures, which corresponds to a maximum deviation not exceeding 0,000 05 in absolute value, and to a relative difference of 0,004 8 %I in relation to the theoretical value. A.4 ACTUAL DEVIATIONS OF THE PREFERRED NUMBFRS A.4.1 In IS0 3, the preferred numbers are given to three significant figures, and the relative difference betw