In this screencast, notice how the [b][color=#1e84cc]base [/color][/b]is a [b][color=#1e84cc]frustum of an [i]elliptical[/i] cone[/color][/b]. [br][br]That is, for [b][color=#1e84cc]this surface[/color][/b], cross sections of planes parallel to the floor and this surface are ellipses.