Using Units in the Metric SI System

A major problem with the customary units is that there is no logical relationship between units. For instance, there is no obvious reason why the standard mile is 5,280 ft. The metric system was created in the late 18th century by the French to address this problem.

One of the advantages of the SI system is that all of the units are based on natural phenomena. For example, a meter is the distance light travels, in a vacuum, in 1/299,792,458th of a second. The U.S. agricultural industry is based on the customary units of measure, however many manufactures are converting to SI units and agriculture has become more international in buying and marketing products. It is critical to understand the differences between the two systems.

In the previous section the several customary units of measure were discussed. The following section will explain the comparable units in the SI system. The SI system is a decimal-based system. To use the different units requires knowing the prefixes used for the different powers of 10, Table 3.1.

Although the recommended practice in the metric system is to use the standard units or 1,000 unit multiples of the units, Table 3.1, there are nonstandard units

TABLE 3.1. Prefixes for SI units.

yotta [Y]

= 1024

yocto [y]

= 10-24

zetta [Z]

= 1021

zepto [z]

= 10-21

exa [E]

= 1018

atto [a]

= 10-18

peta [P]

= 1015

femto [f]

= 10-15

tera [T]

= 1012

pico [p]

= 10-12

giga [G]

= 109

nano [n]

= 10-9

mega [M]

= 106

micro [//]

= 10-6

Kilo [k]

= 103

milli [m]

= 10-3

hecto [h]

= 102

centi [c]

= 10-2

deca [da]

= 10

deci [d]

= 0.1

frequently used in the SI system. It is critical to understand and correctly apply the differences between the U.S. Customary and the SI system, Appendix II.

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