The increased use of S. I. (metric) units adds more need for unit conversion information.

The unit conversions may be between metric and English systems (e.g. meters to feet), different units within a system (square feet to acres, cubic feet to gallons), or from lessor known to more common measurements (pecks to bushels).

For years books of conversions constants, some given free by suppliers, others purchased, that have occupied scientists' and engineers' bookshelves. However, they required the use of a calculator to actually convert a number from one unit to the other. Some calculators now provide conversion capability, however the choice of units is usually not very comprehensive.

Now that many of us use desktop PCs connected to the internet, we can use web sites to access online unit information and calculators. A short cut to a favorite conversion calculator can be placed on your PC's desk top and accessed just as easily as the Windows calculator or other program.

Information About Units

Do you know what a "joch" is? You can find out at a very comprehensive source of information about measurement units provided by Russ Rowlett of the University of North Carolina at Chapel Hill. How Many?, A Dictionary of Units of Measurements , http://www.unc.edu/~rowlett/units/, provides information, in a dictionary form, of a very large number of measurement units. The site contains information about the units used in industry as well as those used in other fields, such as pharmaceuticals and medicine. By the way: a joch is the traditional measurement of land area in Austria, equal to about 1.422 acres.

A source of information about the SI (metric) system from the National Institute of Science and Technology (http://physics.nist.gov/cuu/Units/index.html). This site includes background information on the SI system, SI units and prefixes, definitions, rules and style conventions, guidance on the correct typeface to use for symbols in scientific publications, and much more information. This is an especially useful reference for those writing for scientific publications.

Another useful source of information about SI units is from the French Bureau International des Poids et Mesures , http://www.bipm.fr/enus/3_SI/si.html.

.Frank Tapson provides information about measurement units and conversion between units at http://info.ex.ac.uk/cimt/dictunit/dictunit.htm.

Jacques J. Proot provides some interesting historical perspective on measurement and units, including ancient and biblical usage, at his web site, http://users.aol.com/jackproot/met/index.html.

Conversion Calculators

The real advantage of using a PC connected to the internet is the availability of conversion calculators. These are web sites with forms that allow you to enter a number, the desired unit, and the desired unit. Software at the web site calculates the value corresponding to the new unit.

eFunda inc., a site with extensive engineering information, provides a very complete collection of conversion calculators (http://www.efunda.com/units/index.cfm), including an international currency calculator updated daily. The web site includes mathematical, scientific, and engineering conversions and provides detailed information about each unit and its use. Also included is the ability to search for units. A downloadable Palm version of the units conversion calculator is also included.

Legacy Systems provides an easy to use, although more limited, conversion calculator at http://www.legacysy.com/convert2/convert_old.html.

Process Associates of America provides a simple, easy to use, conversion calculator at http://www.processassociates.com/process/convert/cf_all.htm.

Perhaps the largest collection of calculators on the internet, which includes unit conversion calculators as well as many others, can be found at "Martindale's The Reference Desk, http://www-sci.lib.uci.edu/HSG/RefCalculators.html. Created by James Martndale, a consultant to the University of California at Irvine's College of Medicine, the RefCalculators a part of a larger collection of useful web links.

So the next time you need to convert between joche (plural of joch) and hectares (metric unit of land area), the answer is as close as a web site.