What is the disadvantage in comparing line segments by mere observation?

A line segment is a fixed portion of a line. It starts from a point and ends at a specific point so this makes it possible to measure the line segment. This measure of each line segment is a unique number called its “length”.

The main disadvantage of comparing line segments by mere observation is that we won’t be sure about the line segments of almost same lengths. We will face difficulty in identifying the greater line segment if they are almost same length. Therefore, mere observation is not an appropriate method to compare the line segments.