An interactive applet and associated web page that provide step-by-step instructions on how to construct a perpendicular at the endpoint of a ray using only a compass and straightedge.

The animation can be run either continuously like a video, or single stepped to allow classroom discussion and thought between steps.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.