CIRCLE allows you to select an arc or circle for area and
centroid calculation.

Move the cursor near a desired arc or circle on the 
screen, and press the space bar or cursor button.

For either the arc or circle selected, the area of the
segment is calculated (in the plane of the screen) and
displayed on the prompt line.

Press <Enter> to display the x and y coordinate position 
of the centroid. This position is calculated with respect
to the current view coordinate system (XV, YV) and is 
marked with a temporary asterisk (*).
