 Constants, Units, and Uncertainty  National Institute of Standards and Technology (NIST)
A reference with three sections: Fundamental Physical Constants (values of the constants and related information, and a searchable bibliography on the constants); the International System of Units (indepth information on the SI, the modern metric system), and guidelines for the expression of uncertainty in measurement.
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 A Dictionary of Units  Cleave Books
A summary of units of measurement worldwide (current units and a few of historical interest); conversion factors to the SI (Systeme International); an outline of the SI; its basic defining standards and some of its derived units; all the SI prefixes and some notes on conventions of usage; a short historical note on measures generally; descriptions of the Metric system, the UK (Imperial) system with a statement on the implementation of 'metrication' in the UK, and the US system; and a list of other resources (including other Web sites).
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 How Many? A Dictionary of Units of Measurement  Russ Rowlett; University of North Carolina at Chapel Hill
A dictionary of both metric (SI) and English measurement units, with history, links to related sites, and a bibliography.
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 Measurement Converter  Entisoft Units; ConvertIt.com, Inc.
Many online calculators require a Javacapable browser. Here's one that doesn't, and will perform over 500 different unit conversions for distance, area, volume, mass, speed, temperature, pressure, energy, power, force, etc. And when you convert, say, 5 kilometers to miles, you not only get the conversion result, but a wealth of related measurements and sample conversions.
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 Metrics Matter  ThinkQuest Junior
A simple introduction to the metric system, starting with a basic explanation of how the metric system works. Read about the metric system in relation to other methods of measuring, and learn how to measure time, length, volume, mass, and temperature. Unit conversion calculators show instant results for converting between units, and except for the unit on time, sections give the prefix, abbreviation, and multiplier for the metric measuring units.
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 Metric Week  Math Forum, Teacher2Teacher FAQ
Answers to a frequently asked question: What are some activities I can use for Metric Week?
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 Tables of Roman Measurement  Mike Neill
Tables of Roman measurement on this site (Calender, Capacity, Length, Money, Surface, Weight) are taken from A Smaller LatinEnglish Dictionary, by William Smith LLD, a Classical Examiner in the University of London, John Murray, Albemarle Street, 1865. Tables are generally unaltered except for Neill's conversions from Imperial to metric.
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 The United States and the Metric System  Office of Information Services, National Institute of Standards and Technology (NIST)
A capsule history, with questions and answers, a metric chocolate chip cookie recipe, and some sample size relations (kilogram of butter to pound, etc.).
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