Just for those who don't know a thing about cross sectional areas, I thought I'd explain. A cross sectional area describes the area of a flat (2-dimensional) representation of a 3-dimensional object. So if I cut a cylinder, instead of seeing two circles, I see four circles (unless there are other circles in my environment). The cross-sectional area is the area of either of the two circles. For a cylinder or right solid, the cross-sectional area is the area of the base. For a sphere, the cross sectional area is the area of a circle with the same radius (pi*r2). For an ellipsoid, the cross sectional area is the area of an ellipse with the same long (a) and short (b) axes (pi*ab).