Watch the role of the back cover is fixed movement, dust-proof, waterproof and so on. Made of stainless steel. The back of the corrosive words and patterns,
It and the case generally have three kinds of assembly methods.
1, press the cover directly with the case close (on time) (less waterproof)
2, screw cover and back cover both rib and tighten (waterproof)
3, Rose's case and back cover with Rose fixation, more common in the square case (waterproof)