Though some engineers are oblivious to its existence, there is a system of measurement that has achieved what was once thought of as impossible, true consistency. Taking the base logic of the metric system a step further, this modern means of measurement is known worldwide as "SI" (from the French, Systeme International) and also, in English-speaking countries, as the International System of Units. It is built upon seven base units: the meter (length), the kilogram (mass), the second (time), the ampere (electric current), the kelvin (thermodynamic temperature), the mole (amount of substance) and the candela (luminous intensity). Alone, or in combination, these seven basic units allow anything to be quantified. And though there are many prefixed derivations of these units determined by scale, they all have as their base one of the seven. Furthermore, this method of derivation is such that the system requires no conversion.

Briefly defined, the basic units are as follows. The meter is the length traveled by light in a vacuum during a time interval of 1/299,792,458 of a second. The kilogram has the artifact of a platinum-iridium cylinder as its standard. The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium 133 atom. The ampere is the current that, while held to certain criteria, produces a force equal to two times ten (to the negative 7th power) newton per meter of length. The kelvin is 1/273.16 of the thermodynamic temperature of the triple point of water. The mole is the substance of a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon atoms. Finally, the candela is the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 x 10 (to the tenth power) hertz and that has a radiant intensity of 1/683 watt per steradian.

The units, rules and prefixes that make up SI are meant as a means to facilitate the communication of data worldwide. As such they were designed specifically to suit all languages, to ease mathematics and to avoid ambiguities, all the while retaining some of the traditions of the metric system. If each symbol is written according to SI standards, it will be readable anywhere, regardless of any differences in a nation's language or writing system.

Will SI ever become a worldwide system of measurement? It's hard to say. Most engineers, once they understand the system, value SI for its consistency and its lack of conversion factors. But, then again, there are those who, for either a lack of a need for progress or a curmudgeonly hold on tradition, are slow to recognize its advantage. Of course, this type of resistance is not unusual in the face of any sweeping new concept. After all, rumor has it that the man who first devised the notion of zero was thrown off a cliff.

Sources: Standard Measure
Stan Jakuba
Mechanical Engineering, April 2001
http://www.memagazine.org/contents/current/features/standard/standard.html

NIST Reference on Constants, Units and Uncertainty
http://physics.nist.gov/cuu/Units/background.html