Progression Piece July 1973 | Brentwood, Missouri Oak and Steel | H: 5/13 W: 109/277 D: 3/8 (in/cm)
An arithmetic progression with the bottom edge having an even number (2-4-6-8-10-12-14-16-18)and the top edge an odd number (1-3-5-7-9-11-13-15-17)allowing the bottom to progress steadily beyond the top.