They are supported on hollow steel legs, as long as 57 ft. But the spiral and glass box are close seconds. Ill. Peppa may be overstating, but not by much. Coordinate geometry ruled. Angles and curves intersect all over the place.
Tolerances hover near zero.
Access to the sphere's surface, inside and out, meant jungle gyms of scaffolding. There was lots of field welding. And finishes are high in quality. The atmosphere has been tense and intense. Construction crews had to tiptoe around exhibit crews and a theater team anxious about workers messing up the screen and camera equipment.