Thats right people! the rating on the watch is merely a market descision and not an actual fact of the capacity of the watch in question. This means that the capacity between different watches with the same rating can be significant. one 30 meter watch can vary greatly in maximum capacity from another 30 meter watch(hence the low recommendation for 30-50 m watches in the table above), the same is true with 50 m and 100 m and even 200 m rated watches, infact sometimes the most extreme examples the difference is so great that one watch that is merely rated at 50 or even just 30 meters can compete in capacity with another watch from a different manufacturer that is rated to 100 meter. So the ratings actually don't mean much and is not neccessarly indicative of a watch performance underwater....
That's a shocker is it not?
To use some examples I use Casio and
Suunto. For instance the
Suunto Vector does have a great track record of durability and many people have used it harshly in the field and even used it to make shallow and medium dives down to 15-30 meters(50-100') and yeat it was only tested by
Suunto for a 30 meter rating and according to the recommendation table that means that it should not be submersed at all. An even more absurd example is the new
Suunto Core that also have only a 30 meter rating and yeat is equiped with so called stinger buttons that is made to be used under water and also it comes equiped with a depth gauge so clearly the module and case designers had higher goals for it. Then the marketing department within the company that descided that it should not compete for customers with their more expensive diving computers or the
Suunto Observer and therefor only tested it for a lower rating, a different marketing descision and it could most likely have a 100 meter rating.
This is one of the more extreme examples but it still holds true for all manufacturers. Rating is not an abosulte truth it is merely marketing descisions and the difference in performance between equally rated watches can be great. Other examples is Casio Pathfinder/ProTrek watches that seems very sturdily built and yeat most of them (PAW-1500 beeing the exception) is rated to 100M but would not surprise me if they would survive at 200 meters and therefor compete with many 200 meter watches when it comes to underwater performance.
Another example is Casio G-Shock watches that is rated to 200 meter which is usually the highest rating under ISO 2281. They are inexpensive massproduced watches so if Casio descided to give it a ISO 6425 Divers rating it would increase the cost of manufacturing since then each and every watch has to be subjected to tests, this would increase the cost and hence the consumer price. Therefor (with the exception of the Frogman which is considered a premium G with a higher price point and special dive functions in the module) all G-Shocks are only rated according to ISO 2281 despite the fact that most of them would most likely pass the Divers test with flying colors and several of them would rival the Frogman in under water performance.... once again market descisions descides the rating..... it would not surprise me one bit if many G-Shocks could survive just fine at 300-400 meters water depth its just that they have never been tested by the manufacturer for that level of performance......
The examples I have above are the positive ones where they are underated officially. But it ofcourse goes the other way around as well, most notably are the fragile jewellery and dress watches that probably just barely meet their ratings during the testing, but there is also some surprises for instance the Tissot T-Touch an advanced ana/digi ABC watch that orininally where rated at just 30 meter just like the
Suunto's but that model even though it appears rather rugged looking seems to not be so strong considering the unsual high failure rates in water that model has had.
So the final conclusion regarding ratings is that you should not trust them very much, they don't mean much and is often a mere marketing tool and the difference between models can be great. Infact most of the time we as consumers nor the manufacturers them self knows a particular models maximum performance.
What About Dynamic Pressure?
This perhaps is the biggest myth and urban legend of all. It was mostly created by the watch industry and then spread trough watch retailers and watch brochures and manuals then also trough word of mouth of course. It was not so widespread in the 80's but by the late 90's and early 2000 it had spread alot.
Why they spread that myth to begin with probably have to do with weakening the warranty terms and the fact that they want to encourage people to be carefull with their watches.But also primarly due to marketing reasons that enables them to charge a extra premium for higher rated watches.
Anyway the myth is about movement in water. Apparently as you move around in the water especially your arms an extra pressure gets applied to the watch and the deeper in the water you go the higher this extra presssure will get due to the movement. I have read statements that these movements can add several Bars/ATM/PSI of pressure to a watch. Therefor it is not safe to take your watch anywhere near its stated deepth rating. I have read statements that you should not go any deeper then maximum 30 meter(100') with a 100 m rated watch or 60-70 meter (200-230') with a 200 m rated watch. 30-50 m rated watches should not be submersed at all.
Whats the major problem here?
First let me state that I was a firm believer of this "Dynamic Pressure" myth up untill just a few months ago. This whole journey into this topic for me was the presentation of the
Suunto Core on
Suuntos website prior to its actual release. I thought it looked fantastic and almost imediatly feel in love with it especially in combination with its seemingly superior feature set compared to the competion. Prior to the
Core I pretty muched ruled out
Suunto out of the realm of my interest frame when it came to ABC watches, not because of their active functions which in fact many times where even better then for instance the PathFinders/ProTrek of the Casio line up, but because I saw them as fragile **** due to their poor 30 M water resistance rating(the
Observer with 100 m rating was an exception but did not appeal to me for other reasons). But when the
Core was presented on
Suuntos website it seem to have it all including a 100 meter rating.
But when it was closer to the
Core's release I suddenly noticed that the specs had changed on
Suuntos website now it was suddenly rated to 30 M just like its predeccesor the
Vector so I was very dissapointed and descided to mail
Suunto to get it clarified. Apparently they did a misstake before and that 30 m was the correct fact. But by that time I had already worked up enough interest for the model so that I contemplated buying it anyway, all that I demanded from it was that I could do some surface swimming with it then I would be happy. So I mailed
Suunto and asked again if i could use it when swimming. And the answer was yes!
This confused me because what I knew prior to this told me that 30 m and 50 m watches should not be used for submersive water activitys such as swimming, what confused me even further was the fact that the
Core came equipped with specially designed stinger buttons called UW(Under water buttons by
Suunto) also the demo on the website showed it was also equipped with a cool depth gauge down to 10 meters which further suggested this was a watch that could be used under water.
At first this lead me to believe that
Suunto since it is a special company that has a very scientific image that pride themself with preciscion instruments for professionals was more honest with their rating and therefor took Dynamic pressure into account for their rating and gave their watches a more honest rating then the rest for the watch industry so therefor a 30 M
Suunto was the equvivalent to a 100 Meter watch from other manufacturers.
But this turned out to be a wrong assumption, I later found out that they just test their watches according to the standard ISO 2281 just like the rest of them.
So because I was a believer of the dynamic pressure theory all I was left with was a big mystery, how come a 30 m rated watch was seemingly adapted for underwater use?
This mystery lead me to seek out the answer and learn more about water resistance and the effects of dynamic pressure specifically. I did found some important pieces to the puzzle here in this forum from older forum posts but also from Wikipedia and also some Swedish scientists that I had enquired about this mather.
What I did found out shattered the dynamic pressure theory to pieces. It simply was nothing more then a lie turned into an urban legend and myth.
Apparently pressure can only be applied to an object as the result of added mass/weight that is applied to the object(in this case added depth with an increased weight of the water pillar above you) in question, or as a result of expansion or due to electro magnetism, another possible source of pressure is some external forcing preventing expansion or inversion. Another source is gravitational pull due to accceleration or decceleration but that reason is somewhat tied in to reason number one the one about added mass.