I'm placing this here instead of under Equipment/Computers because the information applies to all dive computers regardless of brand or type, and I believe it's more of an issue for new divers seasoned divers generally become aware (albeit some sooner than others <grin>) of the subject at hand. I apologize for it being so long, and hopefully you can work your way all the way through it.
At some point during your dive training, someone describes the various equipment used, telling you what each item is and what it does. You learn about what an SPG is, what a BC is used for, why you get two regulators, why compasses aren't just for scouts, etc. Dive computers are almost invariably mentioned, along with a statement similar to "dive computers are great because you can dive longer on a computer".
Our time in the underwater universe is limited by essentially two things: air supply and nitrogen absorption. Nitrogen is what "the bends" are about, but you'll probably find that once you're edjumacated you don't call it that very often. In very simple terms, the deeper your dive, the more nitrogen you absorb. The longer your dive (in terms of time) the more nitrogen you absorb. The subject is actually a lot more complex, but keeping in mind the title of this forum and the real intent of this thread, we're just going to leave it at that.
Before dive computers, and for those who dive without them (and believe me, there are thousands and thousands), nitrogen absorption is primarily determined with the use of a table called the Recreational Dive Planner. There are other methods, but we're not going to go into those. You use the table by looking at the maximum depth of your dive and the total length of time of your dive.
Recreational divers usually don't descend to the dive's maximum depth, spend the entire length of the dive at that depth, and then ascend to the surface. A more common dive profile is composed of various depths and times. When you use the RDP, you are determining a 'worst case' by pretending that you were at that maximum depth for the whole time.
A dive computer 'credits' you for those shallower depths by keeping a running tally of your actual depth and time spent. The computer, then, is more realistic, although the worst-case conservatism from the table is lost. This is how you can 'dive longer on a computer'.
I have worked with computers in some form or fashion for almost 30 years. I have worked with them long enough to know to never trust my life to one, at least not if I can possibly avoid it. Computers are designed and built by humans. Humans make mistakes. Ergo (woohoo haven't used that word in a long time) computers can make mistakes. We often think of computers as being smart, but they really aren't. They're the dumbest things on earth. They can only do what they've been told to do, and they make up for dumbness by being really, really fast.
Computers are so embedded in our lives that if you are a passenger on a jet or in a car or on an elevator, you are to some extent trusting your well-being to a computer. However, each of those systems has some sort of backup, be it mechanical or human. Jets these days are actually capable of taking off from an airport, navigating and flying to the destination airport, and landing themselves. But would you get on a jet that had no pilot? How about come snack time, the whole gang left the cockpit and sat down to eat peanuts and watch the movie would you maybe get a little nervous?
I'm not saying to not use a dive computer on the contrary, I have a really nice one that has a feature called 'air integration' the computer is hooked up to my tank so it knows what the tank's pressure is. The benefit to the computer having this knowledge is that it can tell me how much air I have left in terms of time. Even cooler, it gave me real-time biofeedback and taught me how to breathe to achieve maximum airtime. A computer tells you how many minutes you have left in terms of nitrogen absorption, and of course the depth, length, and even the temperature of the dive.
HOWEVER, I know that this is nothing more than a tool of convenience for me, and I do not rely on it to do my dive for me. I know that its airtime remaining estimate is a snapshot of the moment; if I add air to my BC, the estimate is wrong. If I am particularly motionless (not exerting myself) while watching some creature, it's wrong. If I change my depth, it has to catch up. At any moment the computer could 'go on the fritz' completely or, and this is much, much worse, it could experience some sort of hiccup that causes it to give me wrong information. If I've been galavanting around at 80 feet/24 meters for 30 minutes and my computer keeps telling me I've got an hour of no decompression time (the nitrogen absorption thing) left, it's wrong. I have to know all of these things in order to detect the computer's falsehoods and for it to continue to be a useful tool. In other words, you have to understand what it's telling you, why it's telling you that, and when it's anything less than accurate.
The computer manufacturers test the stuffing out of their computers, and generally their reliability is quite high. However, once in a while a series of computers is recalled for some reason or other, and someone had to be the first one to encounter the reason for the recall. Further, the computer manufacturers can't look over your shoulder every day to make sure you're keeping the thing clean and replacing the batteries. Computers are finicky about the quality of their power, and corroded contacts or an aging/defective battery can cause unpredictable results.
Backup equipment is definitely an option but ultimately your best backup is the one between your ears and no amount of equipment replaces it. Use the computer, but don't be dependant on it. You're already smarter than it is, but you need to know at least as much as it does in order to keep your eye on it. You do that by learning how to use your RDP. Use it over and over and over, and you'll find that you'll gain real-time insight into where you are in terms of nitrogen absorption. Take the time and effort to determine your air consumption under different circumstances and take that into consideration in your dive plans. 'Physics' can be a scary word for someone who's not into science and math, but the physics of diving is really not very complicated if you can ballpark a tip for the server at the restaurant and you know when you've been shortchanged by a cashier, you can learn it. It's important to understand why your air supply goes bye-bye a lot faster at 60 feet/18 meters than at 10 feet/3 meters. Get a waterproof watch and independently track the time of the dive.
"To err is human, but to really foul things up requires a computer". The whole reason we take the trip is to watch the movie. But don't forget that you are gonna have to land the plane.
At some point during your dive training, someone describes the various equipment used, telling you what each item is and what it does. You learn about what an SPG is, what a BC is used for, why you get two regulators, why compasses aren't just for scouts, etc. Dive computers are almost invariably mentioned, along with a statement similar to "dive computers are great because you can dive longer on a computer".
Our time in the underwater universe is limited by essentially two things: air supply and nitrogen absorption. Nitrogen is what "the bends" are about, but you'll probably find that once you're edjumacated you don't call it that very often. In very simple terms, the deeper your dive, the more nitrogen you absorb. The longer your dive (in terms of time) the more nitrogen you absorb. The subject is actually a lot more complex, but keeping in mind the title of this forum and the real intent of this thread, we're just going to leave it at that.
Before dive computers, and for those who dive without them (and believe me, there are thousands and thousands), nitrogen absorption is primarily determined with the use of a table called the Recreational Dive Planner. There are other methods, but we're not going to go into those. You use the table by looking at the maximum depth of your dive and the total length of time of your dive.
Recreational divers usually don't descend to the dive's maximum depth, spend the entire length of the dive at that depth, and then ascend to the surface. A more common dive profile is composed of various depths and times. When you use the RDP, you are determining a 'worst case' by pretending that you were at that maximum depth for the whole time.
A dive computer 'credits' you for those shallower depths by keeping a running tally of your actual depth and time spent. The computer, then, is more realistic, although the worst-case conservatism from the table is lost. This is how you can 'dive longer on a computer'.
I have worked with computers in some form or fashion for almost 30 years. I have worked with them long enough to know to never trust my life to one, at least not if I can possibly avoid it. Computers are designed and built by humans. Humans make mistakes. Ergo (woohoo haven't used that word in a long time) computers can make mistakes. We often think of computers as being smart, but they really aren't. They're the dumbest things on earth. They can only do what they've been told to do, and they make up for dumbness by being really, really fast.
Computers are so embedded in our lives that if you are a passenger on a jet or in a car or on an elevator, you are to some extent trusting your well-being to a computer. However, each of those systems has some sort of backup, be it mechanical or human. Jets these days are actually capable of taking off from an airport, navigating and flying to the destination airport, and landing themselves. But would you get on a jet that had no pilot? How about come snack time, the whole gang left the cockpit and sat down to eat peanuts and watch the movie would you maybe get a little nervous?
I'm not saying to not use a dive computer on the contrary, I have a really nice one that has a feature called 'air integration' the computer is hooked up to my tank so it knows what the tank's pressure is. The benefit to the computer having this knowledge is that it can tell me how much air I have left in terms of time. Even cooler, it gave me real-time biofeedback and taught me how to breathe to achieve maximum airtime. A computer tells you how many minutes you have left in terms of nitrogen absorption, and of course the depth, length, and even the temperature of the dive.
HOWEVER, I know that this is nothing more than a tool of convenience for me, and I do not rely on it to do my dive for me. I know that its airtime remaining estimate is a snapshot of the moment; if I add air to my BC, the estimate is wrong. If I am particularly motionless (not exerting myself) while watching some creature, it's wrong. If I change my depth, it has to catch up. At any moment the computer could 'go on the fritz' completely or, and this is much, much worse, it could experience some sort of hiccup that causes it to give me wrong information. If I've been galavanting around at 80 feet/24 meters for 30 minutes and my computer keeps telling me I've got an hour of no decompression time (the nitrogen absorption thing) left, it's wrong. I have to know all of these things in order to detect the computer's falsehoods and for it to continue to be a useful tool. In other words, you have to understand what it's telling you, why it's telling you that, and when it's anything less than accurate.
The computer manufacturers test the stuffing out of their computers, and generally their reliability is quite high. However, once in a while a series of computers is recalled for some reason or other, and someone had to be the first one to encounter the reason for the recall. Further, the computer manufacturers can't look over your shoulder every day to make sure you're keeping the thing clean and replacing the batteries. Computers are finicky about the quality of their power, and corroded contacts or an aging/defective battery can cause unpredictable results.
Backup equipment is definitely an option but ultimately your best backup is the one between your ears and no amount of equipment replaces it. Use the computer, but don't be dependant on it. You're already smarter than it is, but you need to know at least as much as it does in order to keep your eye on it. You do that by learning how to use your RDP. Use it over and over and over, and you'll find that you'll gain real-time insight into where you are in terms of nitrogen absorption. Take the time and effort to determine your air consumption under different circumstances and take that into consideration in your dive plans. 'Physics' can be a scary word for someone who's not into science and math, but the physics of diving is really not very complicated if you can ballpark a tip for the server at the restaurant and you know when you've been shortchanged by a cashier, you can learn it. It's important to understand why your air supply goes bye-bye a lot faster at 60 feet/18 meters than at 10 feet/3 meters. Get a waterproof watch and independently track the time of the dive.
"To err is human, but to really foul things up requires a computer". The whole reason we take the trip is to watch the movie. But don't forget that you are gonna have to land the plane.
, I might even work up a couple of contingency plans & write them on my slate to follow in case the first plan didn't work well with where the cool stuff was - or ask the DM on the way out. On the few wall dives I've done, the DMs gave great briefings on what depths had what features and critters.
