Rounded tetrahedron in epoxy resin satisfying the equation r1+r2+r3+r4=3a where ‘a’ is the length of side of the external tetrahedron, and r1 is the distance from any point p on the surface to the first vertex, r2 the distance from point p to the second vertex, r3 is the distance from point p to the third vertex, and r4 is the distance from point p to the fourth vertex. Designed by Mr. Chris Hoskin, made by Dr. William Tiu of the Engineering Visualisation Research Centre, University of Hertfordshire, 2008.