If you use the overloaded Arc() which takes 8 integer parameters, the first four specify the enclosing rectangle of the ellipse from which the arc is a segment, params 5 and 6 are the start point, and params 7 and 8 the end point. 'Start' and 'end' being counterclockwise movement round the ellipse perimeter.

The parameter that does not have to be given is the centre point of the ellipse (since it can be determined from the first four parameters).

The arc drawn is the curve between the intersection of the (imaginary) start line (centre to start point) with the ellipse, and the intersection of the end line (centre to end point) with the ellipse.