(1) Let \(\over{PQ}\) be the given line segment.
(2) Adjust the compasses up to the length of \(\over{PQ}\).
(3) Draw any line land mark a point A on it.
(4) Put the pointer on point A, and without changing the setting of compasses, draw an arc to cut the line segment at point B.
\(\over{AB}\) is the required line segment.