The SI unit for length is metres. But there is the metric scale (millmetres, centimetres, kilometres) and the imperial scale (inches, miles, yards). It depends upon your preferences.
it is used for measuring length of something
No. Measuring is getting an exact length. Estimating is guessing what the length is
It is necessary because measuring tools help you measure the length of an object accurately.
Use a ruler, measuring tape or other device for measuring length.
For measuring length/distance, meter is used. Other units are km / cm/ mm.
Measuring length
no disadvantage
A ruler.
by measuring it.
There is no such measurement. There is either metric measurement or not. Do you mean "fractions" of inches?
Pythagoras discovered the means for measuring the length of sides of a right angle.
The SI standard unit for measuring length is the meter (m).