Look at the line segments AB and CD shown in the following figure.

Can you say which of the two line segments is longer?

We know a method of comparing the lengths of the line segments i.e., the method of tracing. However, this technique is time consuming since we have to trace the segment each time to compare it with another segment.

There is an even easier way to compare the lengths of two or more line segments with the help of a ruler. A ruler looks like:

The ruler is evenly marked up to 15 units, where the length of each unit is 1 cm.

Each unit of 1 cm is further subdivided into 10 smaller units, where the length of each smaller unit is 1 mm. Thus, there are 10 mm in each centimetre.

Now, let us learn how to use a ruler to compare the lengths of two line segments.