See http://www.rolex.com/watches/datejust-ii/m116300-0007.html
Rolex pretty clearly states that the watch is waterproof. There is also paperwork that comes with the watch stating as such.
You will find somewhere the "Water Resistance" rating. . . This is a Federal Trade Commission requirement. Is it still "waterproof" at the bottom of the Mindinao Deep? I sincerely doubt it. It may be, but it will state "water resistant to 32,000 feet" Some watch maker got sued by the Feds for claiming waterproof without having tested every possible condition. There is a published standard.
OK, I searched Rolex's site. Rolex's are certified "Water Resistant" to 100 meters water pressure. They call that "waterproof" in advertising. . . but not on their watches.
"STRINGENT WATERPROOFNESS TESTING
Defying the elementsAll Oyster Perpetual models are equipped with the Oyster case, providing the movement with optimal protection against water, dust and shocks. Before being shipped, every Oyster watch is immersed in water and subjected to a pressure 10 percent greater than that found at the depth to which it is guaranteed – 25 percent more in the case of divers’ watches. This means that every Rolex Oyster is not just capable of resisting at least 100 metres of water pressure. It has actually done so.
Nothing is “Waterproof” just ask anybody that has ever served aboard a Submarine. That’s why Subs have a Test Depth, they have only been tested to that depth, below that they have a “crush depth”.
You ever watch the scene in Down Periscope where the guy in the engine room runs a string sideways across the sub. As the Sub dives the string begins to sag, the deeper they go, the greater the sag. Eventually the water pressure will crush it, like a tin can.