You may remember the MTM Black Seal from an article we did last month on extreme dive watches. The most notable feature is the fact that it's completely waterproof. What's the difference between being waterproof and water resistant? The easiest way to explain it is that the MTM Black Seal is completely unambiguous in its claims regarding water and pressure resistance: the Black Seal has been proven in a Swiss laboratory to remain fully intact at the deepest known point on earth, the Mariana Trench, which is about 12,000 meters, or about 39,370 feet.