To perpendicular bisector of line segment WX. There are following steps:
1) Draw arcs or circles from points A and B on the both sides of WX.
2) Name the intersection points as W and X.
3) Use the straightedge to draw a line through points W and X.
4) Name the point as O
hence we have construct perpendicular bisector AB of WX which bisects at O.
it would rotate about 180 degrees.