Question

Can u help me with science. what is measurement? what is the need of correct measurement?

Answer 1

If we look at the definition, 
 Measurement can be defined as comparison between an unknown quantity with a fixed/known quantity.

The fixed quantity is called the unit. We must always remember that result of measurement is expressed in 2 parts- a number, and the unit selected for measurement.
 
Example: The length of a pencil is 10cm, 10 is the number and cm is the unit.

Need for correct measurement.
Correct measurement is required so that there is uniformity in the measurement globally. 
For instance, a tailor has to stitch a shirt, if there is no uniformity in the measurement of length, there would be errors.
In scientific research, even more accuracy (much smaller than we can imagine) is required, that is why correct measurements are needed.