Bisect Line with Compass and Straight Edge
This examples shows how to divide a line into two equal parts using a compass and ruler.
Steps

Start with a line with two end points.

Draw an arc outward with a radius equal to the distance between the two points.

Repeat this process with the other point. Label the two points where the arcs intersect.

Draw a line between the two points and label where the line intersects the original line.
We have finished dividing the line into two equal parts.