DIMCENTER DIMENSION Command:

The CENTER dimension command draws a center mark at the center of a selected circle or arc.

select Center Mark under the Dimension Menu,

OR

type dce at a Command: prompt,

OR

click on the the Dimcenter button on the Dimensioning toolbar.

--Prompt: Command: Type dimcenter and press Enter.

--Prompt: Select arc or circle: Click on the edge of the desired circle or arc.

The center mark will appear.