28 - Cardboard sphere
Making a prototype, sketch model, or maquette is often a useful step in identifying at an early stage some of the practical issues that lie ahead.
With fewer constraints e.g., cost, scale, gravity etc, ideas can be quickly realised and a fluidity of thought maintained. Mistakes will have fewer consequences.
Card cuts quickly, and a model can be easily seen from all sides. In this case scissors were used to cut the sections from a cereal packet, and then used to make two parallel slots where the planes intersect. The gap between these cuts is equal to the card thickness; 0.5mm. See slide.
See also; object 24