Nanograms per GramDate: 06/08/2001 at 00:53:11 From: Weston Becker Subject: Mathematical symbols/terminology I am studying some water quality data and have a few questions. First, I understand that if something is a unit is given with a "/" sign then it means "per," e.g. "2 mg/L" means "two milligrams per liter." However, sometimes I see units that say something like "2 ng g-1" (the (-1) portion of this is an exponent). Please explain to me what this phrase is saying. This may be two questions really: what is the relation between "ng" and "g" (per?), and then what does the "-1" exponent mean? Thank you for your help!. Date: 06/08/2001 at 08:41:04 From: Doctor Peterson Subject: Re: Mathematical symbols/terminology Hi, Weston. The exponent -1 means the same thing as the "/", on analogy with ordinary algebra, where b^-1 = 1/b and a * b^-1 = a/b (using our convention of "*" for multiplication and "^" for exponents). So "2 ng g^-1" means 2 ng/g, or 2 nanograms of something per gram of something else. You can read about metric symbol conventions, including this one, here: Using Abbreviations or Symbols - How Many? A Dictionary of Units of Measurement - Russ Rowlett http://www.unc.edu/~rowlett/units/symbol.html Rules and Style Conventions for Printing and Using Units - NIST Guide to SI Units http://physics.nist.gov/Pubs/SP811/sec06.html - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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