10 millimeters (mm.) equal 1 centimeter. 10 centimeters (cm.) equal 1 decimeter. 10 decimeters (dm.) equal 1 meter. 10 meters (m.) equal 1 dekameter. 10 dekameters (Dm.) equal 1 hectometer. 10 hectometers (hm.) equal 1 kilometer. 10 kilometers (km.) equal 1 myriameter. The measures commonly used are the _centimeter_, _meter_ and _kilometer_. _Metric Table of Mass_ (_or Weight_) 10 milligrams (mg.) equal 1 centigram. 10 centigrams (cg.) equal 1 decigram. 10 decigrams (dg.) equal 1 gram. 10 grams (g.) equal 1 dekagram. 10 dekagrams (Dg.) equal 1 hectogram. 10 hectograms (hg.) equal 1 kilogram. 10 kilograms (kg.) equal 1 myriagram. The masses commonly used are the _milligram_, _gram_ and _kilogram_. Notice in these tables the similarity to 10 mills equal 1 cent, 10 cents equal 1 dime, 10 dimes equal 1 dollar, in the table of United States money. Other tables in the metric system are built upon the same plan. Learn the prefixes in order thus: milli, centi, deci, deka, hecto, kilo, myria. The first three prefixes are Latin numerals and represent divisions of the unit. The last four are Greek numerals and represent multiples. In these tables, milli means 1/1000, centi means 1/100, deci means 1/10, deka means 10, hecto, 100, kilo, 1000, myria, 10,000. Two other prefixes are sometimes used, _micro_ which means 1/1,000,000; as microfarad or microvolt, and _meg_ which means 1,000,000, as megohm meaning 1,000,000 ohms. =13. Advantages of the Metric System.=--_First_, it is a decimal system; _second_, the same form and prefixes are used in every table; _third_, the standards of length (meter), volume (liter), and mass (kilogram) bear a simple relation to one another. This simple relation between the three standard units may be given thus: _first_, the liter is a cubic decimeter, and _second_, the kilogram is the mass of a liter of water. (See Fig. 5) Since the liter is a cubic decimeter, the length of one side is 10 cm. The liter therefore holds 1000 ccm. (10 × 10 × 10). Therefore, 1 liter = 1 cu. dm. = 1000 ccm. and since 1 liter of water has a mass of 1 kg. or 1000 g., then 1000 ccm. of water has a mass of 1000 g., or _1 ccm. of water has a mass of 1 g._ [Illustration: FIG. 5.--One liter of the water has a mass of one kilogram.] The following table of equivalents gives the relation between the most common English and metric units. Those marked (*) should be memorized.