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Unformatted text preview: CONVERSION FACTORS The following table gives conversion factors from various units of measure to SI units. It is reproduced from NIST Special Publication 811 , Guide for the Use of the International System of Units (SI) . The table gives the factor by which a quantity expressed in a non-SI unit should be multiplied in order to calculate its value in the SI. The SI values are expressed in terms of the base, supple- mentary, and derived units of SI in order to provide a coherent presentation of the conversion factors and facilitate computations (see the table International System of Units in this section). If desired, powers of ten can be avoided by using SI prefixes and shifting the decimal point if necessary. Conversion from a non-SI unit to a different non-SI unit may be carried out by using this table in two stages, e.g., 1 cal th = 4.184 J 1 Btu IT = 1.055056 E+03 J Thus, 1 Btu IT = (1.055056 E+03 4.184) cal th = 252.164 cal th Conversion factors are presented for ready adaptation to com- puter readout and electronic data transmission. The factors are written as a number equal to or greater than one and less than ten with six or fewer decimal places. This number is followed by the letter E (for exponent), a plus or a minus sign, and two digits that indicate the power of 10 by which the number must be multiplied to obtain the correct value. For example: 3.523 907 E-02 is 3.523 907 10 2 or 0.035 239 07 Similarly: 3.386 389 E+03 is 3.386 389 10 3 or 3 386.389 A factor in boldface is exact; i.e., all subsequent digits are zero. All other conversion factors have been rounded to the figures given in accordance with accepted practice. Where less than six digits after the decimal point are shown, more precision is not warranted. It is often desirable to round a number obtained from a conver- sion of units in order to retain information on the precision of the value. The following rounding rules may be followed: 1. If the digits to be discarded begin with a digit less than 5, the digit preceding the first discarded digit is not changed. Example: 6.974 951 5 rounded to 3 digits is 6.97 2. If the digits to be discarded begin with a digit greater than 5, the digit preceding the first discarded digit is increased by one. Example: 6.974 951 5 rounded to 4 digits is 6.975 3. If the digits to be discarded begin with a 5 and at least one of the following digits is greater than 0, the digit preceding the 5 is increased by 1. Example: 6.974 851 rounded to 5 digits is 6.974 9 4. If the digits to be discarded begin with a 5 and all of the fol- lowing digits are 0, the digit preceding the 5 is unchanged if it is even and increased by one if it is odd. (Note that this means that the final digit is always even.) Examples: 6.974 951 5 rounded to 7 digits is 6.974 952 6.974 950 5 rounded to 7 digits is 6.974 950 Reference Taylor, B. N., Guide for the Use of the International System of Units (SI) , NIST Special Publication 811, 1995 Edition, Superintendent of Documents,...
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This note was uploaded on 02/04/2011 for the course CHEM 101 taught by Professor Dr.n during the Spring '10 term at McMaster University.
- Spring '10