We compared the length of objects.

We lined up their ends to compare.

The blue rectangle is longer than the red rectangle.

The red rectangle is shorter than the blue rectangle.

We used a third object to compare the lengths of 2 objects.

The pen is shorter than the pencil.

The pen is longer than the marker.

So, we know the marker is shorter than the pencil.

Some objects can’t be lined up.

So, we used a third object to compare their lengths.

The leg of the desk is longer than the side of the desk.