![]() The CIPM, and thus this Guide, accepts for use with the SI the units given in Table 7. (h) This unit and its symbol are used to express agrarian area.ĥ.1.2 Electronvolt, astronomical unit, and unified atomic mass unit They depend on the way in which the logarithmic quantities are defined. (g) The numerical values of the neper, bel, and decibel (and hence the relation of the bel and the decibel to the neper) are rarely required. For additional information on the neper and bel, see Ref. ![]() These units are not SI units, but they have been accepted by the CIPM for use with the SI. (f) In using these units it is important that the nature of the quantity be specified, and that any reference value used be specified. If X denotes a mean square signal or power-like quantity, L X is called a power level referred to X 0. Thus when L X = 1 B, X / X 0 = 10, and when LX = 1 dB, X / X 0 = 10 1/10. (e) The statement LX = m dB = (m / 10) B (where m is a number) is interpreted to mean that lg(X / X 0) = m/10. The symbol A is used here to denote the amplitude of a sinusoidal signal, and L A is then called the Napierian logarithmic amplitude ratio, or the Napierian amplitude level difference. (d) The statement LA = n Np (where n is a number) is interpreted to mean that ln(A 2 / A 1) = n. ![]() ![]() However, this unit is called "tonne" in Ref. and ) it is also used in some other English-speaking countries. (c) This is the name to be used for this unit in the United States (see Refs. The script letter ℓ is not an approved symbol for the liter. Thus, although both l and L are internationally accepted symbols for the liter, to avoid this risk the symbol to be used in the United States is L (see Refs. (b) The alternative symbol for the liter, L, was adopted by the CGPM in order to avoid the risk of confusion between the letter l and the number 1 (see Ref. Value of logarythmic ratio quantities such [see footnote (g) regarding the numerical Non-SI units accepted for use with the SI by the CIPM and this Guide Name 8.1 for a suggestion regarding the symbol for year and Chapter 9 for the rules and style conventions for spelling unit names.) In such cases, if a standardized symbol for the unit is not available, the name of the unit should be written out in full. 6.2.8)Īdditionally, this Guide recognizes that situations on occasion will require the use of time-related units other than those given in Table 6 such as using intervals of time be expressed in weeks, months, or years. (The use of SI prefixes with the units of Table 6 is discussed in Sec. The combination of units of this table with SI units to form derived units should be restricted to special cases in order not to lose the advantages of the coherence of SI units. The following four sections discuss in detail the units this Guide accepts for use with the SI.Ĭertain units that are not part of the SI are essential and used so widely that they are accepted by the CIPM, and thus by this Guide, for use with the SI. those units that are not accepted for use with the SI by either the CIPM or this Guide and in the view of this Guide must strictly be avoided. those units that are not accepted for use with the SI by the CIPM, but are temporarily accepted for use with the SI by this Guide and those units that are accepted for use with the SI by the CIPM and hence this Guide Units that are outside the SI, that is, non-SI units, may be divided into three categories: Special Publication 811 (Extended Contents).NIST Guide to the SI, Appendix D: Bibliography.NIST Guide to the SI, Appendix C: Comments on the References of Appendix D - Bibliography.NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science.NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically.NIST Guide to the SI, Appendix B: Conversion Factors Expand or Collapse.NIST Guide to the SI, Appendix A: Definitions of the SI Base Units.NIST Guide to the SI, Chapter 10: More on Printing and Using Symbols and Numbers in Scientific and Technical Documents.NIST Guide to the SI, Chapter 9: Rules and Style Conventions for Spelling Unit Names.NIST Guide to the SI, Chapter 7: Rules and Style Conventions for Expressing Values of Quantities.NIST Guide to the SI, Chapter 6: Rules and Style Conventions for Printing and Using Units.NIST Guide to the SI, Chapter 5: Units Outside the SI.NIST Guide to the SI, Chapter 4: The Two Classes of SI Units and the SI Prefixes.NIST Guide to the SI, Chapter 3: Other Sources of Information on the SI.NIST Guide to the SI, Chapter 2: NIST Policy on the Use of the SI.NIST Guide to the SI, Chapter 1: Introduction.NIST Guide to the SI, Check List for Reviewing Manuscripts.Special Publication 811 Expand or Collapse.
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