Importance of Measurement
Measurement is an integral part of modern science as well as of engineering, commerce, and daily life.
In daily life, the importance of measurement is well known. When we have to bring fruits, vegetables etc. from the market then the seller measures their quantity using beam balance and we have to pay him accordingly. The tailor needs exact measurement  of our body to stitch our dresses. Thus we can conclude that measurement is an essential part of everyday life.

*    Measurement : It is the determination of the dimensions, quantity or capacity of an item.
    Or comparing an unknown quantity with some known quantity is called measurement.

*    Physical quantity : Any quantity that we study in physics ( e.g. length, mass and time) is called physical quantity. A physical quantity is a property of an object that can be measured with a measuring instrument.
    To measure physical quantities such as mass, time and length, we use units such as kilogram, second,  and metre.

*     Unit : A physical quantity (Such as length) has to be measured with respect to some known quantity. This known quantity is called a unit.

Representation of Measurement: 
The result of measurement has two parts; one part is the number and another part is the unit. The known quantity which is used in measurement is called a unit. 
Example; when you say that your height is 150 cm then the measurement of your height is being expressed in a number, i.e. 150 and a unit, i.e. centimeter.