To achieve a particular goal in physics, we usually conducted together with the measurement. Observation of a phenomenon in general is not complete if not accompanied by quantitative data obtained from the measurement results. Lord Kelvin, a physicist said, if we can measure that we are discussing with them and the numbers, we know what we're talking about it.
What do you do when making measurements? For example you measure the length of a table by using the study span, and long tables that span is 6. Thus, the measure is to compare something that is measured with something that is defined as a kind of unit. In the measurement of the above you have to take as a long span. Something that can be measured and expressed with a number called the scale. An example is the scale length, mass, and time. The unit has in general. Have a meter long, has a mass of kg, and has a second time. But later there will be some who do not have the scale unit, such as light refraction index and type of relative mass.
Before the existence of international standards, almost every state set its own system satuannya. The use of various units of a magnitude to cause this difficulty. The first difficulty is requesting a variety of measuring instruments in accordance with the unit is used. Second difficulty is the complexity of conversion from one unit to another unit, for example, to the foot of span. This is not the regularity of the set-conversion unit is.
Due to hardship caused by the use of a different system then the ideas appear to menggunkan only one type of unit only for the scale-scale in science and technology. An international agreement has set a single international system (International System of Units) unit abbreviated SI. SI unit is taken from the metric system that has been used in France.
