Machinery's Handbook, 31st Edition
2000 CALCULATING THREAD DIMENSIONS Calculating and Rounding Dimensions Rounding of Decimal Values.— The following rounding practice represents the method to be used in new or future revisions of ASME B1 thread standards. Rounding Policy: When the figure next beyond the last figure or place retained is less than 5, the figure in the last place retained is kept unchanged. Example: 1.012342 1.01234 1.012342 1.0123 1.012342 1.012 When the figure next beyond the last figure or place retained is greater than 5, the figure in the last place retained is increased by 1. Example: 1.56789 1.5679 1.56789 1.568 1.56789 1.57 When the figure next beyond the last figure or place retained is 5, and: 1) There are no figures, or only zeros, beyond the 5, the last figure should be increased by 1. Example: 1.01235 1.0124 1.0123500 1.0124 1.012345 1.01235 1.01234500 1.01235 2) If the 5 next beyond the figure in the last place to be retained is followed by any fig ures other than zero, the figure in the last place retained should be increased by 1. Example: 1.0123501 1.0124 1.0123599 1.0124 1.01234501 1.01235 1.01234599 1.01235 The final rounded value is obtained from the most precise value available and not from a series of successive rounding. For example, 0.5499 should be rounded to 0.550, 0.55 and 0.5 (not 0.6), since the most precise value available is less than 0.55. Similarly, 0.5501 should be rounded as 0.550, 0.55 and 0.6, since the most precise value available is more than 0.55. In the case of 0.5500 rounding should be 0.550, 0.55 and 0.6, since the most pre cise value available is 0.5500. Calculations from Formulas, General Rules.— 1) Values for pitch and constants derived from a function of pitch are used out to eight decimal places for inch series. The eight place values are obtained by rounding their truncated ten place values. Seven decimal place values for metric series constants are derived by rounding their truncated nine place values. Values used in intermediate calculations are rounded to two places beyond the number of decimal places retained for the final value, see Table 1 and Table 7. 2) Rounding to the final value is the last step in a calculation.
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