## How Many? A Dictionary of Units of Measurement © Russ Rowlett and the University of North Carolina at Chapel Hill Table of Contents About the Dictionary Using the Dictionary Using the Dictionary

This dictionary includes:

• all the units of the International System of Units (SI);
• many other units of the metric system used in everyday life or in science, either currently or recently;
• various non-metric scientific units such as the astronomical unit, the electronvolt, and the parsec;
• all the units of the English traditional systems I've encountered that can be defined with reasonable precision;
• selected traditional units from cultures other than English; and
• certain measurement terms and notations which are not "units of measurement" in a strict sense, but which are used much as if they were.

Each unit's definition includes conversion factors you can use to convert that unit into other units measuring the same concept. In the case of the traditional units, remember that in many cases the "precise" definition for an older unit (such as the league or the hogshead) was not established until the nineteenth century. It's not wise to rely too much on these definitions when reading older works. Also, many units which have precise meanings now, such as the barrel and the gallon, formerly had a variety of special meanings when applied to particular commodities; there isn't space in the dictionary for all these meanings.

For many units, an abbreviation or symbol is given in parentheses, like this: gram (g). Generally speaking, symbols do not appear as separate entries, except in those cases where one could not guess from the symbol which page the unit appears on. So if all you know is a symbol or abbreviation, it's necessary to scan the appropriate page and search for the abbreviation. For example, for the unit abbreviated "Pa" look on the "P" page.)

It is often necessary to use scientific (powers of ten) notation, like this: 106. If that doesn't show up on your screen as 10 raised to the 6th power, then similar problems will occur throughout the dictionary.

In addition, there are several Greek letters used as symbols. Most Internet browsers use Unicode encoding and will display the "micro" symbol µ (lower case Greek letter mu) and Greek letters such as π (lower case pi), γ (lower case gamma), and Ω (capital omega).

The dictionary observes certain standard conventions on using numbers and units.

The dictionary contains a huge number of links intended to cross-reference between units. If you find such a link that doesn't work, please let me know so I can fix it.