To construct a series of parallel cross-sections of a solid you make use of the properties of planes and secants in a solid:
secants of several cross-sections in the same plane are parallel;
secants of a certain cross-section in parallel planes are parallel.
Sometimes you need to draw such a series of parallel cross-sections life sized.
A series of parallel cross-sections often gives a good impression of the shape of the solid. Below you see a series of parallel cross-sections of a pyramid and a plane perpendicular to the base and parallel to two edges of the base.