ClipArt ETC
"DE being chosen as an isometric line or axis, a second axis, YY, is drawn isometrically perpendicular to it. Points C and F lie on this axis, and their position is readily determined, since measurements may be made on this line. As line AB, drawn through C, is an isometric line, points A and B may be located at their proper distances to the right and left of the axis YY." —Anthony, 1904

Pentagon Elevation and Projection Scaling

"DE being chosen as an isometric line or axis, a second axis, YY, is drawn isometrically perpendicular…