Praise and suggestions from Edward Tufte on the iPhone.
Look for a not unexpected shot at Powerpoint at about the halfway point.
(There seems to be no way to embed the video, so please visit the official site to view.)
The chair has three upholstered pieces, each attached to a curved plywood shell. The larger one is the seat; the smaller two are back supports. All three are strategically angled to maximize your comfort. Charles and Ray Eames, the husband-and-wife design team behind the chair, had a remarkable understanding of ergonomic principles long before these were developed into a science in the 1970s.