What does a unidirectional rotating bezel mean on a watch?

　　What does a unidirectional rotating bezel mean? If you have questions about this, let us take a look below.

　　Dive watches are generally equipped with a unidirectional rotating bezel (Unidirectional Turning Dive Bezel). In addition to its decorative and symbolic modern concept of an active lifestyle, the raised markers and highly legible numerals on the bezel allow the wearer to accurately adjust dive and sports times with absolute reliability. The outer bezel only rotates in one direction; even if it is accidentally turned, the remaining sports time will only be shortened, not lengthened, ensuring safety. It generally rotates unidirectionally to a certain scale (irreversibly) so that divers can determine their oxygen consumption and the time to return to the surface based on the watch's indication.

　　Principles of watch water resistance

　　To test the water resistance of a watch, it is placed in a sealed container filled with water. The container is pressurised to 3 atmospheres within 1 minutes, held for 10 minutes, and then returned to normal pressure within 1 minutes. The watch is then removed and checked for water ingress. Since 1 atmospheres is equivalent to a water depth pressure of 10 metres, a watch that passes the 3 atmosphere test is marked as 30 metres water-resistant.

　　But why is there such a significant difference between the marked depth and actual use? Firstly, standard pressure tests are merely static measurements, where pressure is increased to the marked level within a few seconds. However, when worn by a user, the environment the case is subjected to is dynamic. The hand is the part of the body that moves most frequently; whether in daily life or water activities, the limbs often make large movements. Even for recreational scuba divers diving within 30 metres, the rapid ascent and descent create frequent changes in pressure.

　　Can watch water resistance be trusted?

　　How did a timepiece with a water resistance depth of one hundred metres let water in at eighty metres?

　　Speaking of depth, if you are not a professional diving enthusiast, you probably do not know how many metres you have descended. For those of you mostly just splashing around in shallow water areas, a basic waterproof watch with a rating of fifty or sixty metres is enough for your use. Of course, because of this, you have no way of knowing the accuracy of the value.

　　In fact, in watch testing and measurement, the waterproof depth expressed in metres is merely a theoretical value. Waterproof depth refers to the water resistance when both the watch and water are completely stationary. This stationary condition does not exist in the real world for swimmers or divers. So when you put on your 100-metre deep-water resistant watch, make sure you do not get carried away and swim down to a depth of 100 metres.

　　Friends around me often ask questions like this. The paradox of complete water resistance versus water ingress frequently occurs. According to guidelines issued by the US Federal Trade Commission, watch sellers must not label their watches as completely water-resistant.

　　Meanwhile, certain timepieces such as the Rolex Submariner and Blancpain Fifty Fathoms are deep-diving watches manufactured specifically for deep diving. Although their water resistance has reached an exceptional level, even claiming they can stay in the deep sea for a period without issue, they still cannot be termed completely water-resistant.

　　You would be far too easily swayed to dismiss the idea of buying a water-resistant watch just by seeing the two points above. The primary function of a good water-resistant watch is water resistance, and consumers can fully consider what kind of water-resistant watch to buy based on their usual lifestyle and wearing habits, whether it is basic daily water resistance, swimming water resistance, or deep-diving water-resistant watches. Although the standard values cannot be trusted implicitly, they also indicate a range of instructions for use, so there is no need to worry too much when purchasing.