Length Metres, litres, kilograms

 2 a . Metre. The French National Assembly ordered the French Academy of Sciences in Paris to design a system of measurement that would be easy to use and suitable for everybody. In 1791 it established the length unit, its name would be metre and it would be the ten-millionth part of the distance from the North Pole to the Equator. That is, the distance from the North Pole to the Equator divided into ten million parts. In order to establish this distance they did the necessary measurements and they made the metre standard, which is a bar of that length. The metre standard is kept in the International Bureau of Weights and Measurements in Paris. Nowadays, for the distance metre not to depend on an object that can deteriorate, the metre is defined using the light speed for reference. It is the distance travelled by light in absolute vacuum in 1/299792458 of a second.

2 b . Multiples and submultiples of the metre.

To express distances larger and smaller than the metre more accurately, the multiples and submultiples of the metre were established by adding some Greek and Latin prefixes.
The value of the units go from ten to ten, the same as our numeration system. This makes unit conversion easier.

The symbols are not abbreviations, you should write them as they are presented in the table, with no capital letters, without a dot and without adding -s, even when they are used in plural.

 Prefix Name of the unit Symbol For the multiples kilo- meaning 1000 times kilometre km hecto- meaning 100 times hectometre hm deca- meaning 10 times decametre dam base unit metre m For the submultiples deci- meaning the tenth part decimetre dm centi- meaning the hundredth part centimetre cm milli- meaning the thousandth part millimetre mm

These units are used most frequently but there are others, too: you have probably heard of the micron or micrometre, used to express the size of viruses and cells. The micrometre is also a submultiple of the metre, it is the thousandth of a millimetre, thus it is the millionth part of a meter.

In order to express a measurement you have to use a single unit, you can say "I'm 1,70 m tall" or "I'm 170 cm tall." However, it is better not to say "I'm 1 m and 70 cm tall."

When measuring, you have to strive for accuracy, clarity and order, you have to use the measurement device suitable to the accuracy needed.

Taking a measurement wrongly can mean you have to repeat an activity all over again.

Esta unidad interactiva requiere la máquina virtual de Java J2RE.

 Here, the units are out of order, you have to put them in descending order by dragging them to the top.

 Eduardo Barbero Corral Spanish Ministry of Education. Year 2007