Dive Computers vs. Dive Tables

Is it Dive Computers vs. Dive Tables or is it Dive Computers and Dive Tables?

Before dive computers became a common sight in the scuba scene, the only reliable way to calculate safe dive times were dive tables. Dive tables were initially created for military use in order to ensure that divers don’t suffer from decompression sickness.

Dive Table and Dive Computer Basics

Dive tables are setup under the assumption that the scuba diver stayed at the maximum depth for the entire dive. The nitrogen absorption is calculated based on these parameters.

PADI Recreational Dive Table

Dive computers work differently. They record the actual time and depth of a scuba diver and then calculate the nitrogen absorption based on these actual values. This higher level of accuracy results in longer dive times and shorter surface intervals.

Different Bottom Time Results

The differences in the calculations can be quite astonishing. If you for example take a dive at 120 feet. Based on dive tables you can stay down for around 10 minutes as the assumption is that you spend the whole dive at 120 feet. A dive computer will take the actual values into consideration and you’ll end up with a bottom time of around 30 minutes (or so). Quite a difference…

In any typical scenario the safety margins with dive computers are much higher than with dive tables as the parameters used for the calculations are the actual values and as the calculations are continuously being performed. With a dive table you typically have to figure out beforehand how long you can stay at what depth while the dive computer adjusts the nitrogen absorption calculations on the fly. It can then provide information about decompression stops on the way up if necessary.

One of the big drawbacks of both dive tables and scuba computers is that the calculations are based on mathematical models. The diver’s physical data like weight, etc. is not taken into consideration. This means that neither method completely eliminates the risk of decompression sickness. It can be safely assumed that one of the next generations of dive computers will take these physical parameters into consideration for even safer and more accurate calculations.

Many dive computers allow to adjust their algorithm with safety settings. It would always be a wise choice to use a safer setting rather than an aggressive setting to calculate nitrogen absorption.

Deepest Dive First - Still the Rule?

When relying on dive tables it was always a rule to have the deepest dive first and shallow dives following later. With modern dive computers this rule is no longer required. They can calculate reverse dive profiles exactly and the same as traditional dive profiles. However, when relying on dive tables, you can’t do a reverse dive profile. When you do a shallow dive first and follow that with a deep dive, you either end up with a decompression stop or you couldn’t even calculate your bottom time as the dive tables won’t support this scenario. You can safely dive such a profile if you use a dive computer as it will calculate correctly.

Many new divers wonder why they even should care about dive tables when the dive computer does all the work. This is true to some extent but it can also be dangerous to not know the basics and not know how to use a dive table.

Why even consider dive tables?

Unfortunately, dive computers, as any other device, can break or in the simplest case, run out of battery. If at that time you don’t know how to use a dive table, you’ll be stranded until your computer is fixed or the battery is replaced. A diver knowing how to use dive tables can use this method as a backup in case the dive computer stops working.

A counterargument might be in this case that you could have a backup dive computer that can be used. While this is true, it also has a risk factor involved. The backup dive computer does not know anything about your previous dives and thus might end up with calculations that could put you at risk for decompression sickness. It will be safer in that case to use dive tables as you can adjust those to take your previous dives into consideration.

Best Practice – Be able to use both

A best practice is to use a dive computer as your main calculation tool and dive tables as your backup. A personal dive computer allows you to keep a lot of your dives. Many of the modern dive computers can transfer that log to a computer and you can model future dives based on that historic data.

The capabilities offered by such a personal scuba computer are infinitely higher than what you could accomplish with the use of dive tables and manual logs. However, to keep your dive experience safe you should have a basic understanding of the models used to calculate dive times.

Dive Computers can do what Dive Tables can’t

Dive computers not only made it more convenient to dive but also offer dive profiles that were practically not possible by only using dive tables. Well, they were possible but the time it took to plan a dive was enormous.

Many modern dive computers for example allow to switch gases on the fly so you can use different nitrox mixes or use air and nitrox in a single dive to maximize your bottom time. Higher end models also allow to measure air consumption to further maximize and optimize any dive.

Conclusion

Dive computers are essential to the safety of the sport. Over time they became reliable devices that maximize bottom time while providing higher margins of safety for the diver. No diver should go diving without a personal scuba computer. However, to always be on the safe side and to understand what a dive computer is really doing, it is highly recommended to know how to use dive tables. One never knows when it becomes necessary to use them.

Enjoy your diving and go get a dive computer if you don’t have one. Check out our guide to the best dive computers so you can find the best device for your budget and diving needs!

Image Credit: https://www.flickr.com/photos/61438018@N00/2279256524​

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