The Seven chair is Mart van Schijndel's reinterpretation of Gerrit Rietveld's Zigzag chair.
In Rietveld's revolutionary design a two dimensional plane is "folded" to create a three dimensional object: a chair without legs. Look at it from the side and the silhouette is indeed a zigzag; a line that follows the X and the Y axis. The chair does not actually change directions in a 3D space. That is the challenge Mart van Schijndel put himself to when he designed the Seven chair: Adding the Z axis. In that sense the Seven chair can be seen as a unique conceptual breakthrough and a worthy homage to the old master Rietveld.
Only very few Seven Chairs were made and even less survived. It is a conceptual chair, which is quite fragile and should be treatd as a sculpture, rather than a seat.