Yabba-Dabba-Dive: Why We Still Teach Tables in the Age of the Beeping Wrist Computer
Benjamin Hadfield Oct 06, 2026
Yabba-Dabba-Dive: Why We Still Teach Tables in the Age of the Beeping Wrist Computer
By Benjamin Hadfield
I read the SDI/TDI article “Dive Computers vs. Dive Tables.” The horse-and-buggy and stone-tablet joke made me smile. And to be fair, the article says tables are not obsolete and still have a place. I agree with that. Where I part company is the idea that because computers do the calculations, divers don’t need to understand the ideas behind them.
I have taught open-water for a long time, and (yes) I still teach the actual tables, BUT I don’t expect anyone to carry a stone slab to the boat and chisel out a dive plan before the captain calls “DIVE, DIVE, DIVE”. I do expect divers to have their computers ready, in functional mode, not locked out from the previous day, and know how to use them. But a computer is a tool. It does not take responsibility for the person wearing it.
A computer can tell you that you have 12 minutes of NDL remaining. It can’t tell you whether spending those 12 minutes is a good choice for you, your buddy, and the rest of your dive day. That takes a little understanding.
The computer is the tool. The table is the lesson and understanding.
A dive table makes the relationship between depth and time visible. As depth increases, the time available within a given NDL limit decreases. Longer bottom time changes the calculation. Make another dive, and the first dive you made matters a great deal.
A computer shows the result quickly. A table makes a diver work through the relationship. They look at planned depths, find the corresponding limit, and see how the pieces fit together. That turns “an NDL of 28 minutes” from a mysterious number on a screen into a concept they can explain.
Recreational tables assume a square profile: reach the planned depth and stay there for the planned time. That makes them more conservative than a computer following a multilevel profile, where the diver moves through several depths, with remaining at the maximum planned depth of the dive only a portion of the total dive. The computer is now able to take into account the time that is NOT spent at that depth and return that unspent time to the diver in additional available NDL. A table is a planning model with assumptions. It is not a perfect replay of every real dive.
But the square profile is also useful for teaching. It gives the class a clear, conservative baseline. A diver can compare that baseline with a computer’s changing readout and ask, “Why is my computer giving me more time? What part of my profile is it counting? How much margin am I leaving?” Those are better questions than, “The screen isn’t providing any warnings yet, so I’m good, right?”
In an era of the ever-growing distrust of Artificial Intelligence, the blind trust many divers hand over to their dive computer and the lack of understanding behind its proceedures, methods, conservative settings, and general settings is nothing short of mind-blowing.
The “I was just doing what my computer said” should be enough to give any Divemaster a sudden cold shiver of fear.
NDL does not mean “go until the computer yells”
The NDL limit is a boundary in a decompression model. Staying within it means the model does not call for mandatory decompression stops on ascent, assuming the diver follows the applicable procedures. It does not mean no decompression stress, and it is not a guarantee against DCS. Think of it like this: these limits are there to help keep you safe and are just like the RPM limiter on your vehicle. Just because your tach ‘CAN’ go to 6,500 RPM doesn’t mean it's a good idea to run it to that limit every time you go to the grocery store. A little conservatism can, and does, go a long way. At least with your car, you can replace the engine. This is your only body that you’ll be given; treat it with a little kindness.
That distinction matters. A diver can start treating the NDL like a target: stay down until the number gets small, then come up when the computer starts sounding like a smoke alarm with an attitude. The computer may still be doing exactly what it was designed to do. It is the diver who has mistaken a limit for a goal.
DAN says DCS can happen after dives that remain within computer or table limits. The models estimate risk from information such as depth, time, and breathing gas, but cannot account for every factor affecting a person’s decompression stress. A DCS hit within the displayed limits does not become “undeserved” in the sense of being impossible or inexplicable. The word describes a dive with no obvious limit violation; it does not mean the diver had no risk.
The “undeserved hit” and the diver who keeps shaving off the margin
Here is the part I want divers to take seriously. A 2025 DAN article by hyperbaric physician and dive instructor Nick Bird identifies staying close to NDLs across a dive or a series of dives as a likely contributor to many DCS cases he sees. A diver may remain inside the computer’s displayed limits and still take on more decompression stress than a table-based plan would allow. Risk increases as a diver gets closer to the NDL; the computer does not turn that risk into zero just because the countdown has not reached zero.
I am not saying every DCS case comes from a diver pushing the limit. It doesn’t. Susceptibility differs, and conditions such as cold, exertion, depth, profile, and previous dives matter. I am saying that “I was still within my computer’s limit” does not end the conversation.
Some divers set the computer to a less conservative option, then use every minute it offers. Others leave the settings alone but make a habit of taking the NDL down to the last few minutes, dive after dive. The screen can make that feel tidy: 10 minutes, 5 minutes, 1 minutes. It is tempting to think the computer has measured the diver’s personal safety margin down to the last minute. It has not. It is displaying the output of a model.
The same pattern can carry over to repetitive dives. A diver reaches the limit on dive one, takes what feels like a decent surface interval, then does it again on dive two. Each dive may show “within limits.” But the exposure is accumulating, and the margin may be shrinking. DAN’s point is not that the computer failed. It is that following the computer right to its edge is not the same as diving conservatively.
That is where a look at the tables can be sobering. Put the planned maximum depth and time into the appropriate table. Work through the repetitive-dive procedure. See what pressure group and residual nitrogen time the plan produces. A student may find that the day’s plan uses most of the table’s allowance—or that the proposed repetitive dive leaves little room under that table’s rules. That gives them a concrete picture of how aggressively they are planning.
A table cannot tell us precisely how close someone was to a DCS injury. It is not a medical risk meter, and its limits are not interchangeable with every computer’s algorithm or settings. But it can make the lack of margin hard to ignore. That matters. A table lesson can turn “I’m still technically inside the computer’s limit” into “I am choosing to spend nearly all the allowance this model gives me.” That should make a diver stop and think. Fred Flintstone might still say, “Yabba-dabba-doo.” I’d like him to say it with a few minutes left on the clock.
The second dive starts before you splash
Residual nitrogen is another reason tables are worth teaching. After a dive, the body is still eliminating inert gas. A surface interval allows some of that gas to leave, but it does not reset the diver to a fresh, never-dived state.
Repetitive-dive tables represent this continuing exposure with a pressure group and, depending on the table, residual nitrogen time. A longer surface interval gives the model more time for off-gassing before the next dive. A shorter interval leaves more residual nitrogen in the calculation and less available no-decompression time.
That is a simple idea, but it is easy to lose when all the diver sees is a new number on a screen. The second dive is not automatically a clean slate because lunch was good and you did a backflip off the back of the boat. The first dive matters.
A table exercise lets students plan the whole day: What is the first dive? How long is the surface interval? What depth is planned for the next dive? What does the first dive do to the second one? If the plan changes, what needs to be reconsidered? Those questions build divers who pay attention to the whole series, not just the next splash.
Nitrox is helpful. It is not a cheat code.
Nitrox is a good example of why the underlying ideas matter. At the same depth, enriched air has a lower nitrogen fraction than air, so the model calculates less nitrogen exposure. That can be used to reduce decompression stress on a given profile or to extend no-decompression time. You cannot claim both benefits at once. DAN describes the same trade-off: dive nitrox to air limits to retain a margin, or use the equivalent air depth to extend bottom time and spend that margin.
A table lesson helps explain equivalent air depth: nitrox changes the nitrogen calculation; it does not make the diver physically shallower. Nitrox also brings oxygen limits. Divers need to know the mix, its maximum operating depth, and the relevant oxygen partial-pressure limit. Their computer must be set for the gas they are actually breathing. A computer with the wrong mix entered can produce very convincing numbers for the wrong gas. That is not the sort of confidence we need underwater.
The point is not that every diver must calculate every nitrox dive by hand. The point is that when a computer shows more no-decompression time on nitrox, the diver should understand why—and remember that the extra time does not cancel the oxygen-depth limit.
Better technology still needs a thinking diver
A computer’s real advantage is that it follows the diver’s changing depth and time profile. It can update the NDL, provide ascent-rate information, and record the dive. That is why I want students to learn their computers well: how to set the gas, read the display, recognize alarms, understand ascent guidance, and use the manufacturer’s instructions.
But “computer” does not mean “one universal answer.” Different computers use different models and settings. They do not directly measure nitrogen in a diver’s tissues; they estimate decompression status from the information available to them. They also do not know the diver’s full health, fitness, exertion, or thermal situation.
Computers are wonderful tools. They are not tiny dive doctors strapped to your wrist. They cannot see you shivering, fighting current, or trying to keep up with a buddy while your workload climbs. They cannot know that you are tired or that you have decided the last six minutes of NDL are “basically free.” The screen needs a diver who understands what it can—and cannot—tell them.
Tables help teach that judgment. They also help divers understand why no-decompression limits deserve respect, why surface intervals matter, and why repeated dives close to the edge can add up. NOAA’s Diving Program still lists air and nitrox tables as resources for calculating maximum depths and dive intervals. Tables are still used; the Stone Age has not quite claimed them.
If the computer fails, don’t improvise a new plan
Tables also belong in a discussion about backup planning, but let’s be careful here. A diver should not lose a computer halfway through a repetitive-dive day, grab a table, and start guessing. A table is useful only if the diver has tracked the exposure and knows how to apply the correct system. DAN warns against casually switching between computer and table calculations during a dive series when the full profile has not been accounted for. If the diver does not know their decompression status, guessing is not a backup plan.
That is another reason to teach the tables: divers should know what information matters and how much they are relying on the computer. The right backup plan is made before the failure, not while everyone is waiting on the surface and one diver is trying to remember which way the table folds.
Bring back Bedrock—for the lesson
I am not asking anyone to replace a dive computer with a stone tablet. I want divers to use their computers and understand them. I also want them to know what depth, time, NDL, nitrox, residual nitrogen, and surface interval mean before those ideas become a string of numbers on a screen.
The table may be old technology. The relationships it teaches are still part of diving. A few minutes with one can help a diver see when a plan is getting aggressive, especially when they are using the computer’s full allowance over several dives. It will not predict a DCS hit or tell us exactly how close someone came to one. It can show that the diver left very little margin—and make “I was still within my computer’s limit” sound less like a force field.
Fred and Barney can leave the stone tablet at home. The lesson still comes along.
