About Drafting References
You can specify a drafting reference depending upon the type of draft entity that you want to create. The following drafting references are available on the Sketch tab, in the Controls group:
• 
Angle
Angle• 
Offset
Offset• 
References
References• 
Radius
Radius• 
Start Tangency
Start Tangency• 
End Tangency
End Tangency• 
Absolute Coordinates
Absolute Coordinates• 
Relative Coordinates
Relative Coordinates