Within the tough outer steel shell is another structure made of a lighter gauge material. (treehugger.com)
It has a mechanical watchface and circular dial covered in sapphire mirror glass, a silicon strap, and a stainless steel shell boasting waterproofing at up to 50 meters. (androidheadlines.com)
Now imagine that the planet gets completely surrounded by a thin black steel shell, located a few thousand metres above the surface, as shown in a cutaway view in the picture above, and in Figure 1 below. (wattsupwiththat.com)