To Create a Construction Line
Construction geometry entities are lines and circles that you can use to locate and create 2-D draft geometry. They appear on the screen in phantom font, but you can transfer them through IGES files and plot them.
1. Click Legacy Sketch tab and choose one of the following operations:
◦ Click 
Construction Line–creates a single line.
Construction Line–creates a single line.◦ Click 
Crossed Pair–creates two construction lines perpendicular to each other, intersecting at the pick point.
Crossed Pair–creates two construction lines perpendicular to each other, intersecting at the pick point.The Snapping References dialog box opens. If you want to specify an entity to use for an offset or angle base, click the arrow in the dialog box, and then select the entity. The entity is highlighted and added to the list or references.
2. Click a start point for the line. The line will span the display and pass through the pick point.
3. Place the second point of the line freehand, or right-click and select Offset, Angle, Absolute Coordinates or Relative Coordinates commands on the short cut menu to enter precise centerpoint or angle values, using your selected references.