The metric system, or the International System of Units (SI) as it is now known, is a worldwide standard measuring system based on scientific, non-changing, decimal units of measure. Its origins can be traced as far back as the 16th century, with formalization beginning in the late 1700s. The development and refinement of this system continue today.

Significance
The metric system is a profound achievement, in that it stipulates seven basic units of measure that cover length, time, mass, temperature, substance amount, light intensity and electric current. From these seven, all other metric units can be derived. Scientists have in the metric system a standard set of measurement tools that are the same worldwide, and everyone has a simple and scientific system to measure whatever could possibly need to be measured.

Effects
Humans have long recognized the need for standardized measurements. Using grains of barley, the span of your hand, foot size and the length between elbow and fingertip may have been fine for some cultures and times, but for this age of rapidly developing technologies and global communication and collaboration, only the standardized metric system has proved sufficient.

History
First steps toward the metric system were made in 1585 by Simon Stevin in his book "The Tenth," according to the U.S. Metric Association's chronology of the metric system. Stevin suggested a decimal system--based on the number 10--for measuring.

The next step forward came in 1670 when a French astronomer, Gabriel Mouton, proposed "a comprehensive decimal measurement system based on the length of one minute of arc of a great circle of the Earth," according to the article "A Brief History of Measurement Systems" found on NASA's website.

Formalization
But real progress was not made until the French Revolution. In 1799, a platinum bar one meter long and a platinum kilogram were placed in the Archives de la Republique in Paris. France adopted the decimal metric system in 1795, and made its use mandatory in 1840.

Thirty-five years later, the Convention of the Metre (or the Treaty of the Meter) was signed in Paris. This established the General Conference on Weights and Measures (CGPM), which coordinates international standardization of weights and measures.
Development of the system continued. By 1960, the International System of Units was named and the meter, kilogram, second, ampere, Kelvin and candela had been established as base units in the decimal metric system. The seventh basic SI unit, the mole, was approved in 1971.

Global Adoption
All industrialized countries of the world have now wholeheartedly adopted the metric system except the United States, even though the U.S. was one of the 17 nations that signed the Treaty of the Meter in 1875.

But even in America, foot-dragging progress continues. The metric system is the obvious tool for scientific and medical work. Many food products are labeled in metric units. And the U.S. stock exchange finally converted to decimal trading in 2001.