# How the Metric System Works

Metric System: Risks and Rewards

If taking a tour of SI units and prefixes hasn't convinced you of the metric system's advantages, then tackle this exercise: convert 5 miles to inches. Quick. In your head. Even if you remember how many feet are in a mile (5,280) and how many inches are in a foot (12), you still have some complex arithmetic to do. Here's what the math would look like:

(5 miles)(5,280 feet/1 mile)(12 inches/1 foot) = 316,800 inches

The metric system makes life much easier. A similar conversion would be to find how many centimeters exist in 5 kilometers. A kilometer is 103 meters; a centimeter is 10-2 meters. To make the conversion, you simply move the decimal point to the right five times:

5 kilometers = 5,000 meters = 500,000 centimeters

See why SI units are easier?

Because of its elegance and simplicity, the International System of Units can be found throughout the world. The United States is the only industrialized nation that still clings to its legacy measures and, as a result, wrestles with a confusing array of unrelated units. Of course, cost factors into why the U.S. has been slow to adopt the metric system. As an example, consider NASA's space shuttle program, which still adheres to the inch-pound system of measurement. NASA engineers recently reported that converting the relevant drawings, software and documentation to SI units would cost a total of \$370 million -- a big chunk of change, even for a government agency that easily spends \$760 million to get a shuttle into the air [source: Marks].

Of course, not converting comes with its own financial risks. Take NASA again. In 1999, the space agency lost its \$125 million Mars Climate Orbiter probe when a unit mismatch caused a malfunction [source: Marks]. The mismatch occurred because its attitude-control system used imperial units, but its navigation software used SI units. As a result, the probe swung too close to the planet, overheated and then ceased to function properly. Now it's a million-dollar piece of space junk, thanks to America's lagging commitment to SI.

Many U.S. companies have paid attention to these cautionary tales. John Deere, Proctor & Gamble, Kodak, Ingersoll-Rand and numerous other businesses have converted all or some of their operations to use SI units. That means their overseas factories and supply chains use the same measuring system -- and the same parts -- as their American counterparts. That may seem minor, but the savings can be significant. Cost reductions come from two principal sources: increases in productivity resulting from the use of a decimal-based measurement system and the ability to compete more effectively in global markets.

Eventually, the U.S. will make the metric system compulsory for its citizens. When that time comes, it will change the look of road signs, gas pumps and food labels, but it won't affect some hallowed expressions. Why? Because a country kilometer and a 30-centimeter-long hotdog simply don't echo the American experience.

### Sources

• Alsdorf, Matt. "Why Hasn't the U.S. Gone Metric?" Slate. Oct. 6, 1999. (Sept. 14, 2011) http://www.slate.com/id/1003766/
• International Bureau of Weights and Measures. "The International System of Units -- and the 'New SI ...'" (Sept. 14, 2011) http://www.bipm.org/en/si/
• Marks, Paul. "NASA criticised for sticking to imperial units." New Scientist. June 22, 2009. (Sept. 14, 2011) http://www.newscientist.com/article/dn17350-nasa-criticised-for-sticking-to-imperial-units.html
• "metric system." Encyclopaedia Britannica, 2011. Web. (Sept. 14, 2011) http://www.britannica.com/EBchecked/topic/378783/metric-system
• National Institute of Standards and Technology. "The United States and the Metric System: A Capsule History." Oct. 4, 2006. (Sept. 14, 2011) http://ts.nist.gov/weightsandmeasures/metric/lc1136a.cfm
• Nelson, Robert A. "The International System of Units: Its History and Use in Science and Industry." Via Satellite. February 2000. (Sept. 14, 2011) http://www.aticourses.com/international_system_units.htm
• Physical Measurement Laboratory of NIST. "The NIST Reference on Constants, Units and Uncertainty: International System of Units (SI)." Oct. 2000. (Sept. 14, 2011) http://physics.nist.gov/cuu/Units/
• Rowlett, Russ. "How Many? A Dictionary of Units of Measurement." Center for Mathematics and Science Education, University of North Carolina at Chapel Hill. July 11, 2005. (Sept. 14, 2011) http://www.unc.edu/~rowlett/units/index.html
• Smith, David. "Metric Conversion: How Soon?" Public Roads. Summer 1995. (Sept. 14, 2011) http://www.fhwa.dot.gov/publications/publicroads/95summer/p95su14.cfm
• Sobel, David. "The Kilogram Isn't What It Used to Be -- It's Lighter." Discover Magazine. March 8, 2009. (Sept. 14, 2011) http://discovermagazine.com/2009/mar/08-kilogram-isn.t-what-it-used-to-be-it.s-lighter/?searchterm=SI
• Taylor, Barry N. and Ambler Thompson, eds. "The International System of Units (SI)." NIST Special Publication 330. 2008 Edition. (Sept. 14, 2011) physics.nist.gov/Pubs/SP330/sp330.pdf
• U.S. Metric Association. "Metric System Information." (Sept. 14, 2011) http://lamar.colostate.edu/~hillger/