From a point on a line:
 

Procedure: From a point on line AB strike two equidistant arcs, a' and b'. From the points of intersection of these arcs with line AB strike two intersecting arcs of equal radius. Connect the intersection of these arcs to form the line CD. This line will pass through the original point at an angle perpendicular to AB.

From a point to a line:
 

Procedure: From point C strike an arc through line AB. From the points of intersection a' and b' strike two intersecting arcs of equal radii. Connect the points of intersection of these two arcs and extend the line to point C. Line CD will be perpendicular to line AB.