Chapter 7-PRINC[PLES OF MEASUREMENT 



or psi) is equally acceptable and is very com- 

 monly used. Similar conversions can be made 

 for any of the other units, as long as the basic 

 relationships of the system are accurately main- 

 tained. 



When converting values from a metric sys- 

 tem to a British system (or vice versa) it is 

 necessary to understand the units used in each 

 system. Most of us know quite a bit about the 

 units commonly used in British systems, but 

 less about the units used in metric systems. 

 A description of the basic structure of the metric 

 systems follows. 



All metric systems of measurement are 

 decimal systems— that is, the size of the units 



vary by multiples of 10. This makes computa- 

 tions very simple. Another handy thing about 

 the metric systems is that the prefixes for the 

 names of the units tell you the relative size of 

 the units. Take the prefix kilo-, for example. 

 Kilo-indicates 1000; so a kilogram is 1000 

 grams, a kilometer is 1000 meters, and so forth. 

 Or take the prefix milli-, for another example; 

 it indicates a thousandth. So 1 millimeter is 1 

 thousandth of a meter, 1 milligram is 1 thou- 

 sandth of a gram, and so forth. Perhaps the 

 best way to become familiar with the units in 

 the metric systems is to associate the more 

 commonly used prefixes with the positive and 

 negative powers of 10, as shown in table 7-2. 



Table 7-2. —Metric System Prefixes and Corresponding 

 Positive and Negative Powers of 10. 



METRIC SYSTEM PREFIXES 



POSITIVE AND NEGATIVE POWERS OF 10 



DEKA- or DECA 



HECTO- 

 KILO- 



10 



10 



10^ 



10 

 100 



1000 



MEGA- 



10 



1, 000, 000 



DECI- 



10 



0. 1 (or 1/10) 



CENTI- 



10 



0.01 (or 1/100) 



MILLI- 



10 



0.001 (or 1/1000) 



MICRO- 



10 



0.000001 (or 1/1,000,000) 



123 



