Context: 
The figure below shows an example of creating a rectangular datum coordinate
  system defined by two lines. 
  

When 
  Abaqus/CAE
  prompts you to select an edge, you can select one of the axes of a datum
  coordinate system. 
 
  
	 From the main menu bar, select
		.
	 
	 
The Create Datum dialog box appears. The dialog
		box outlines the types of datum geometry you can create.
	 
	 Abaqus/CAE displays prompts in the prompt area to guide you through the procedure.
	 
	 
		
	 
   
  
	 From the list of types at the top of the dialog box, choose
		CSYS.
	 
	 
The Method list indicates the methods you can
		use to create a datum coordinate system.
	 
   
  
	 From the Method list, select 2
		lines.
	 
	 
Abaqus/CAE
		displays the Create Datum CSYS dialog box.
	 
   
  
	 From the dialog box, enter the name of the datum coordinate system. 
	 
	 
To help keep track of your datum coordinate systems, 
		Abaqus/CAE
		displays its name in the 
		Model Tree.
		In addition, you can use the 
		Model Tree
		to rename the datum coordinate system. 
	 
   
  
	 From the dialog box, select one of the following datum coordinate
		systems:
	 
	 
		
 
		  -  
			 
Rectangular: The
				X-, Y-, and
				Z-axes are aligned with the 1-, 2-, and 3-global
				axes, respectively.
			 
 
		   
 
		  -  
			 
Cylindrical: The
				R-, -,
				and Z-axes are aligned with the 1-, 2-, and 3-global
				axes, respectively.
			 
 
		   
 
		  -  
			 
Spherical: The
				R-, -,
				and -axes
				are aligned with the 1-, 2-, and 3-global axes, respectively.
			 
 
		   
 
		
	 
   
  
	 From the Create Datum CSYS dialog box, click
		Continue.
	 
  
 
   
	 If desired, select Make Independent from the
		prompt area to create the datum as an independent feature. 
	  
  
 
 
  
	 From the part or assembly in the current viewport, select a straight
		edge that will define the X- or
		R-axis of the datum coordinate system.
	 
  
 
  
	 Select a straight edge that will lie in the
		X–Y or -plane.
	 
	 
The datum coordinate system appears. You cannot move or rotate a
		datum coordinate system.