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Discussion Starter · #1 ·
The rotating bezels on dive watches always seem to have the first 15 minutes more precisely deliniated than the other 45. Can anyone tell me why? It seems like the first 15 minutes underwater using a tank would be the least important to track, not the most important. If anything, shouldn't the numbers on the bezel be a countdown instead of a countup? If the numbers started at 60 and then worked down to 1, then when the minute hand hit the 15 you'd know you have 15 minutes left. When it hit the 10, 10 minutes left, etc. I've never seen it explained how to use the numbers on the rotating bezel, but it seems to me that it would be more useful as a countdown.
 

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I'm not a diver, so this isn't the authoritative answer, but my understanding is that you set the number of minutes down time on the bezel, and then the number shows how much longer you can stay down.

There are a number of models that have the countdown as you describe - my Hamilton is one.

 

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the "countdown" red zone as some call it dates back to when divers used specific Navy Tables to plan a dive to a specific bottom time. some used to turn the point of the bezel (O) to the desired exit time before going in then the countdown zone gave you a timer to start your ascent.. might not be exact on the explanation but what I remember since the explanation wasn't part of our training but just "what the Navy guys used to do" in the early days of diving.

more commonly for the last 50 years or so let's say you begin your dive at 10 minutes till 4, you turn the bezel to point to the "10"... then at a glance you can tell how long you've been down versus what the tables said your max time at depth was to stay in a non-decompression status. you don't have to remember what time you started your dive, it's marked for you. I've used the old countdown timer in the past to check my rate of ascent as in seconds.. computers have changed all of this, most people don't even wear a dive watch any longer.. but I do.

short answer, it's an antiquated method of timing ascents while marking your exit time on a planned dive instead of marking time of entry method of timing your planned dive table dive and is still included on some timing bezels as a nod to the past.:thumbup1:
 

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Discussion Starter · #4 ·
Thanks for the answers, but it still makes no sense to me that it would be the first 15 minutes/seconds that are more precisely marked. In your example, if you set the point of the bezel to the time you want to exit, does that mean that the 15 minutes/seconds after the 0 are more clearly marked so you can see how long you've overstayed your estimated time down? If you set it so that the marker is where the minute hand was when you started your dive, the first 15 minutes would be more precisely marked rather than the last, more critical minutes!

I think the Hamilton shown makes much more sense. If you want to stay down 40 minutes, set the bezel so that the minute hand is on the 40, then at a glance you can see how much time you have remaining, which seems more convenient than having the bezel tell you how long you have been down. Since most dives are longer than 15 minutes, I don't see how the more precisely marked first 15 minutes would ever be of use. What I find really interesting is watches that have carried this over as a pure fashion statement. No rotating bezel, inner or outer, but the minute markers from 1 to 15 are a different color and have more pronounced markers at every minute than those starting at 16.
 

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I think you misunderstood what our qualified diver was saying. You set the bottom time on the bezel at e minute hand, and then the last 15 minutes are graduated to help you plan your ascent and holds at depth.
 

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yes, what t/c said..

I never used this method, I was not a Navy Diver in the 50's so my explanation is just what we were told during training as a "this is what the Navy used to do" and was not taught that method at all. matter of fact in recreational scuba diving this method of timing dives and ascents was frowned upon and seen as dangerous. the method of planning your dive, marking your time before you enter the water was seen as a much more conservative way, another reason a real dive watch has a counterclockwise rotating bezel only.. to assure a conservative timed dive.

seems like someone has a better explanation for this outdated method, I don't doubt this..
as a PADI Certified Master Scuba Diving Instructor I never tried to explain this during training nor did anyone ever ask that I remember.:blink:

fashion statement and/or a nod to the past (Rolex or Fifty Fathoms, don't remember) is all it is nothing more.
 

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Discussion Starter · #11 ·
Can you give me an example? For example, bottom time is ?, so you set the bezel so that the minute hand points to ?. Then, during the last 15 minutes, the minute hand moves from the 1 on the bezel to the 15 on the bezel.
Thanks!

I think you misunderstood what our qualified diver was saying. You set the bottom time on the bezel at e minute hand, and then the last 15 minutes are graduated to help you plan your ascent and holds at depth.
 

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Discussion Starter · #12 ·
Are you saying that using current safety procedures the rotating bezel has no use? The only thing I can see that it is good for is keeping track of elapsed time, in which case it is the first 15 minutes that are graduated, which doesn't seem helpful at all. I can see a use for elapsed time, but having the first 15 minutes be graduated seems silly, unless I really am just not getting this.

yes, what t/c said..

I never used this method, I was not a Navy Diver in the 50's so my explanation is just what we were told during training as a "this is what the Navy used to do" and was not taught that method at all. matter of fact in recreational scuba diving this method of timing dives and ascents was frowned upon and seen as dangerous. the method of planning your dive, marking your time before you enter the water was seen as a much more conservative way, another reason a real dive watch has a counterclockwise rotating bezel only.. to assure a conservative timed dive.

seems like someone has a better explanation for this outdated method, I don't doubt this..
as a PADI Certified Master Scuba Diving Instructor I never tried to explain this during training nor did anyone ever ask that I remember.:blink:

fashion statement and/or a nod to the past (Rolex or Fifty Fathoms, don't remember) is all it is nothing more.
 

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Interesting question...and answers. I speculate that it's because most dives last less than 20 minutes, due to air tank capacity. I also speculate that there's a huge dose of 'that is how we always did it' thrown in for good measure. Caution: I do NOT claim to be authoritative in any way; I am merely sharing an opinion.
 

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Are you saying that using current safety procedures the rotating bezel has no use? The only thing I can see that it is good for is keeping track of elapsed time, in which case it is the first 15 minutes that are graduated, which doesn't seem helpful at all. I can see a use for elapsed time, but having the first 15 minutes be graduated seems silly, unless I really am just not getting this.
today, most divers don't even wear a watch as a timing device any longer... they use a computer that times the dive and computes the bottom time available based on a multi level dive profile. but that wasn't your original question, the red zone or the first 15-20 minutes usually marked in minutes or red is useless and is basically just a nod to the past (Navy method countdown ascent timer) and holds no significance at all. particularly with recreational divers.

the counterclockwise rotating timing bezel however is still a fine backup timing device to a computer in general.

lets say using the dive tables you've calculated your profile and you are able to dive to a specific depth for 35 minutes. before starting your dive you simply rotate the bezel where the marker ^ points to the current position of the minute hand.
you know the amount of bottom time the tables said you had at the planned depth, you dive your dive periodically checking the elapsed time by counting the minutes indicated by the marks/numbers on the bezel and with all factors considered you make sure with the proper ascent time and rules for safety stops that you return to the surface in the original calculated allotted time.
now we have computers that calculate all of that without having to really refer to dive tables because all of that is figured in the computer along with actually knowing how deep you are, when your dive started and how long you've been down, even figuring multi level diving profiles for more accurate calculations. some computers are air integrated and figures everything down to how much nitrogen you should have accumulated in your blood.. that's the main purpose of all of this timing is keeping track of how much excess nitrogen or oxygen you have accumulated and allow for off gassing before reaching the surface again.
note: the timing bezel just keeps up with the amount of bottom time you have calculated with the dive planner (tables) at the depth you planned to dive, it does not keep up with how much air you breathe from the tank, for that you have to monitor your tank pressure gauge.. so there's many reasons why just anyone can't walk up and rent a tank and jump in the water, a proper underwater scuba training course is needed to understand fully the inherent dangers of scuba diving.
 

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Interesting question...and answers. I speculate that it's because most dives last less than 20 minutes, due to air tank capacity. I also speculate that there's a huge dose of 'that is how we always did it' thrown in for good measure. Caution: I do NOT claim to be authoritative in any way; I am merely sharing an opinion.
:thumbup1:
for sure every dive is different with depth in direct correlation to the rate of consumption of compressed air, enriched air, or mixed gas. I'd guess out of the hundreds or thousands of dives I've completed (recreational scuba) the average time was probably 35-40 minutes of bottom time. conceivably a person could dive some locations that may have a sand flat bottom of 30-33 feet and could stay down for hours if you had the tank capacity. I remember the longest dive I made to this day was on Palancar/Paradise Reef Cozumel lasted approximately 68 minutes, with a max depth of 60 feet maybe with the profile slowly ascending to about 35 feet. again, the deeper you go the faster you breathe down your air... one dive off Punta Sur (Devil's Throat) I hit a max depth of 142' and total dive time with 3 sets of safety stops (because I broke the tables) was about 38 minutes, I was lucky I had air because i had to drop below the planned depth by about 20' to get a narc'd diver that was slipping off into the abyss.. her mother would not have been happy with me had I not brought her back breathing I'm afraid.

all the rules are very structured in recreational diving training, there are just a lot of factors that figure into trying to stay safe, along with certain practices such as setting your computer a bit conservative to build in a fudge factor because every person off gasses at slightly different rates.. and experience. so in my mind conservative is the way to go.
 

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Discussion Starter · #16 · (Edited)
Thank you for the excellent explanation! I feel much better about the fact that it never really made sense to me. I think I'm usually pretty good at figuring things out. I started to suspect that it was not very useful when I began to see the first 15 minutes on non-dive watches either a different color or more prominantly marked - and not even on a bezel, but on the actual dial. I've seen some watches that I otherwise liked, but just couldn't bring myself to buy because they were obviously trying to look dive-ish while not being the least bit dive-y. I agree that for general use it's nice to have a rotating bezel to determine how much time either remains or has lapsed, but now I'd rather they made the first 15 minutes just the same as the other 45.

As for the dangers of diving, are you saying that sharks aren't all you have to worry about? (Kidding of course). I have always wanted to dive, but the only times I've been in a place where it might be interesting I was either on my honeymoon with a wife who won't go in the ocean, couldn't afford the extra expense, or was recovering from surgery. Honeymoon was Jamaica, which would have been perfect, although in addition to it being our honeymoon our budget was pretty tight, the others were Hawaii - The Big Island, Kauai, and Oahu. So the only time I've used scuba equipment was in a friend's swimming pool. We were sanding some damaged areas on the bottom of his pool and would have never gotten it done if we had to come up to breathe.


today, most divers don't even wear a watch as a timing device any longer... they use a computer that times the dive and computes the bottom time available based on a multi level dive profile. but that wasn't your original question, the red zone or the first 15-20 minutes usually marked in minutes or red is useless and is basically just a nod to the past (Navy method countdown ascent timer) and holds no significance at all. particularly with recreational divers.

the counterclockwise rotating timing bezel however is still a fine backup timing device to a computer in general.

lets say using the dive tables you've calculated your profile and you are able to dive to a specific depth for 35 minutes. before starting your dive you simply rotate the bezel where the marker ^ points to the current position of the minute hand.
you know the amount of bottom time the tables said you had at the planned depth, you dive your dive periodically checking the elapsed time by counting the minutes indicated by the marks/numbers on the bezel and with all factors considered you make sure with the proper ascent time and rules for safety stops that you return to the surface in the original calculated allotted time.
now we have computers that calculate all of that without having to really refer to dive tables because all of that is figured in the computer along with actually knowing how deep you are, when your dive started and how long you've been down, even figuring multi level diving profiles for more accurate calculations. some computers are air integrated and figures everything down to how much nitrogen you should have accumulated in your blood.. that's the main purpose of all of this timing is keeping track of how much excess nitrogen or oxygen you have accumulated and allow for off gassing before reaching the surface again.
note: the timing bezel just keeps up with the amount of bottom time you have calculated with the dive planner (tables) at the depth you planned to dive, it does not keep up with how much air you breathe from the tank, for that you have to monitor your tank pressure gauge.. so there's many reasons why just anyone can't walk up and rent a tank and jump in the water, a proper underwater scuba training course is needed to understand fully the inherent dangers of scuba diving.
 

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sharks are not a lot of fun but through the years the waters I have been in, you usually see their tail fin going away from you. (except that one time) being in water with you're ability to breathe through a regulator only, there's more to it than meets the eye. all the physics involved, and all the stuff that can get you, basically you don't want to touch anything because it might hurt you or you may damage or kill it. it's been fun though, nothing like it.
 
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