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Engineering notation is a version of scientific notation in which the exponent of ten must be divisible by three (i.e., they are powers of a thousand, but written as, for example, 106 instead of 10002). As an alternative to writing powers of 10, SI prefixes can be used, which also usually provide steps of a factor of a thousand.〔Except in the case of square and cubic units: in this case the SI prefixes provide only steps of a factor of one million or one billion respectively.〕 On calculators, engineering notation is named "ENG". Compared to normalized scientific notation, one disadvantage of using SI prefixes and engineering notation is that significant figures are not always readily apparent. For example, 500 µm and 500 × 10−6 m cannot express the uncertainty distinctions between 5 × 10−4 m, 5.0 × 10−4 m, and 5.00 × 10−4 m. This can be solved by changing the range of the coefficient in front of the power from the common 1–1000 to 0.001–1.0. In some cases this may be suitable; in others it may be impractical. In the previous example, 0.5 mm, 0.50 mm, or 0.500 mm would have been used to show uncertainty and significant figures. It is also common to state the precision explicitly, such as "47 kΩ ±5%" Another example: when the speed of light (exactly by the definition of the meter and second) is expressed as 3.00 × 108 m/s or 3.00 × 105 km/s then it is clear that it is between 299 500 km/2 and 300 500 km/s, but when using 300 × 106 m/s, or 300 × 103 km/s, 300 000 km/s, or the unusual but short 300 Mm/s, this is not clear. A possibility is using 0.300 Gm/s, convenient to write, but somewhat impractical in understanding (writing something large as a fraction of something even larger; in a context of larger numbers expressed in the same unit this could be convenient, but that is not applicable here). Engineering notation, like scientific notation generally, can use the E notation, such that :3.0 × 10−9 can be written as :3.0E−9 or 3.0e−9 The ''E'' or ''e'' should not be confused with the exponential ''e'' which holds a completely different significance. In the latter case, it would be shown that 3e−9 ≈ 0.000 370 23. ==See also== * Significant figures * Scientific notation * Binary prefix * International System of Units (SI) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「engineering notation」の詳細全文を読む スポンサード リンク
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