ON ARC allows you to select an arc or circle on which to
create a point entity.

Select the desired arc or circle.

Enter an angle (in degrees) at which you want to place the
point on the selected entity. This angle is 
counter-clockwise, relative to the zero (0) position on 
the arc. It is not necessary to specify an angle between 
the start and endpoints of the arc. The arc does not
necessarily need to lie in the current display plane.

The point entity (+) is created in the plane of the arc's
depth, regardless of the status of the 2-D/3-D switch.
