I often get asked just how tough (the case and bracelet) the metal Dia-Schild and Duratec (scratch-resistant) metal truly is.
I created a chart for easy reference.
They are lined up in order of toughness according to Hv (Vickers Hardness) ranking system.
They get tougher the further you go to the right.
"DiaShield" is about 2-3 times harder than Stainless Steel.
"Duratect/DLC" is about 5-7 times harder.
"Duratect α" is about 10 times harder. It is the same as Sapphire crystal.
It is used in models such as the AT9050-58A "Citizen Exceed".
There is this much of a difference between Seiko and Citizen.（SEIKO may currently be developing new technology.）
The DLC(Diamond-like Carbon) doesn't mean that is is just as hard as a diamond、but that it has a structure similar to a diamond.
As a final note, even though they are tough to scratch, it doesn't mean that they can't be.