You can use the CenterMark command to create a center cross or center line at the center of a circle or arc. 

The display of the Center Mark is defined in the current dimension style under radial dimensions.


How to create a Center Mark:

  1. Click on Dimension > Center Mark on the Ribbon.

or

  1. Enter CENTERMARK in the command window.
  2. Click on a circle or an arc in the graphics area.