Principles of naval engineering - Historic Naval Ships Association

Chapter 7-PRINC[PLES OF MEASUREMENTor psi) is equally acceptable and is very commonlyused. Similar conversions can be madefor any of the other units, as long as the basicrelationships of the system are accurately maintained.When converting values from a metric systemto a British system (or vice versa) it isnecessary to understand the units used in eachsystem. Most of us know quite a bit about theunits commonly used in British systems, butless about the units used in metric systems.A description of the basic structure of the metricsystems follows.All metric systems of measurement aredecimal systems— that is, the size of the unitsvary by multiples of 10. This makes computationsvery simple. Another handy thing aboutthe metric systems is that the prefixes for thenames of the units tell you the relative size ofthe units. Take the prefix kilo-, for example.Kilo-indicates 1000; so a kilogram is 1000grams, a kilometer is 1000 meters, and so forth.Or take the prefix milli-, for another example;it indicates a thousandth. So 1 millimeter is 1thousandth of a meter, 1 milligram is 1 thousandthof a gram, and so forth. Perhaps thebest way to become familiar with the units inthe metric systems is to associate the morecommonly used prefixes with the positive andnegative powers of 10, as shown in table 7-2.Table 7-2. —Metric System Prefixes and CorrespondingPositive and Negative Powers of 10.METRIC SYSTEM PREFIXES POSITIVE AND NEGATIVE POWERS OF 10DEKA- or DECA101010100HECTO-KILO-10^1000MEGA- 10 1, 000, 000DECI- 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