Perpendicular line
The Perpendicular Line 
tool is used
to create a line perpendicular to an existing line or arc.
Using the mouse
Select the Perpendicular Line tool and type in the length value.
Then click on an existing line or arc to select the base point for the perpendicular line.
Move the mouse to set the direction of the perpendicular line, and click to position the line.
Using the keyboard
After selecting the Perpendicular Line tool, type in the length value.
Move the mouse to set the direction of the perpendicular line, and click to place the perpendicular line.
Hold Ctrl while placing the second point to draw the line symmetrically in the opposite direction, with the base point at one end.