SPECIAL GUEST POST: Dive Computers or Dive Tables? That is the Question

The author after receiving her Open Water Scuba Instructor certification in southern Mexico near Tulum.  Author’s bio, Social Media links, and business contact at the end of the article.  Photo courtesy of the author.
PUERTO RICO — Dive Computers or Dive Tables?  That is the question… No need to think too much about the most popular and probably best answer: Dive Computer.  Yes, a Dive Computers will make your diver-life much easier; it eliminates much of the time you need to plan a dive, its algorithm allows you to get more out of your dives, more bottom time and less surface time between immersions (Surface Intervals).  They come with all sorts of different, convenient features, and depending on the model and price range there are an incredible array of options to choose from: you have the very basic computers, and others with different settings like Enriched Air or “EANx,”some that automatically adjust for altitude, type of water, etc.  Some are more conservative than others, and some you can adjust the algorithm to be more or less conservative.  All new computers will measure your depth and time underwater and quite a few other variables with greater precision than old fashioned tables and analog gauges.  However, no matter what you choose as your dive computer remember: Always read the manual before use!
Now, that I sound completely on the side of Dive Computers let me tell you why you should understand and use Dive Tables.  Why have the tables become so unpopular?  Well, because of computers, obviously!  But do you know that tech divers use dive tables along with carrying more than one computer? Why would they do that?
The author, Christina Lorenzo, underwater near her home in Puerto Rico.  Photo courtesy of the author.
Because even the best of computers can fail.  The most simple recreational dive can go wrong and the types of deep and complex dives inherent to the tech diving world have added risks of their own, they’re deep!  They’re complicated!  More pressure, more risk!  Dive equipment is made to last, but nothing is perfect and the more complicated the dive the more that can go wrong.  But this is why I would argue that even recreational divers who never plan to go very deep or penetrate caves or wrecks should still pay what amounts to professional attention to their knowledge and equipment.  I don’t mean that every recreational diver should sport two (or three) computers, four cutting devices, and carry a canister light with two backups–rather to approach one’s own training and gear with a serious eye.  Scuba diving is great fun but it does carry some inherent risks: risks that can largely be mitigated by good training and proper knowledge.
As a professional diving instructor I’ve learned not to continue a dive with only the Table if the computer fails.  If your computer fails you should end that dive.  However, you can definitely use Dive Tables for the rest of the days you’ll be diving.  Also Dive Tables or RDP/eRDPml are great to understand and make use of, if your computer is not built with EANx and, or Altitude settings.   No matter what you choose, you have to learn to read (and understand) both: your Computer(s) and the Table(s).  
Recently I took the Altitude Diver Specialty in Lake Atitlán in Guatemala with ATi Divers (big shout out to the only dive shop around the lake and my Instructor Daniel who is an RDP genius)!  Being a “sea-level” Caribbean, shallow-water  instructor myself, I had pretty much put the Tables in a trash can until the day I had to learn to read the RDP Table in a theoretical manner for the Altitude Specialty.  It fascinated me and finally I can say I understand them and their importance.  In conclusion, exercising  your mind and keeping it at work should never be a thing of the past!

Christina Lorenzo Agront.  Photo courtesy of the author.
ABOUT THE AUTHOR — I recently met Christina Lorenzo at La Iguana Perdida in Santa Cruz la Laguna, Guatemala where she was working on her Altitude Specialty.   Christina, who is currently back in Mexico working on her Master Scuba Diver Trainer rating, wrote the following article as something of a companion piece to my last article on dive watches following discussions we had on diving and, ideally, how one should train.  Christina is one of those restless, polymath adventurers you seem to meet at places like Lake Atitlan.  Based out of Rincon and Aguadilla Puerto Rico, she ran track and field in college, was part of the national Roller Derby team, traveled to Dallas for the Roller Derby World Cup, established herself as a hairdresser with a specialty in colorimetry, and discovered scuba diving through her clients.  She decided to go for dive certification in Mexico close to the cenotes she’d been wanting to see for years.  The pandemic lock-downs were starting and she booked the very last flight from the closest airport before travel was shut down for over a year.  “That was the best decision of my entire existence,” she told me, adding, “I met Xibalba through the cenotes, did my Rescue Diver course with a local crocodile, dived the second largest coral reef in the planet, and wrecks, and caverns… I became a Divemaster and finally an Open Water Scuba Instructor.  On a recent trip to Guatemala’s Atitlán Lake, I found a place where you can feel inspired again, it made me realize I could take my diving farther than just Open Water Scuba Instructor.  Life is too brief to just dream about what one could have achieved.”  
Follow Christina on Instagram at scuba_closet and her website www.scubacloset.com.  Contact her via e-mail about diving and dive training in Puerto Rico at scubacloset@gmail.com or by phone at 01-787-452-8415

The Dive Watch: a real tool for the scuba diver or relegated to desk duty?

By Andrew J. Tonn

Guatemala City — Whether you ever take them underwater or not, these are three purpose built dive watches more than capable of use as a scuba diving tool. While dive computers have rightfully superseded using a waterproof watch with a timing bezel (the Doxa also includes the U.S. Navy no-decompression table on the outer bezel ring) and dive tables to track your dives, a good dive watch is a great backup timing device. In many cases it is also quicker and easier to get your elapsed time with a glance at your watch, and every diver should learn how to use dive tables in order to understand what their computer is doing. From left to right: The Seiko Prospex SRP777 “Turtle”, The Deep Star 1000 from Deep Blue Watches, and the Doxa Sub 750T Professional. Shown with a vintage Wenoka diver’s knife, a Poseidon BlackLine mask, and Pelican 1150 case. Photo taken with a Fuji XT-4 and Fujinon 35mm f/2 lens.

GUATEMALA CITY — Is the dive watch still valid as a tool for scuba divers?  The short answer is yes.  It absolutely is.  Before I begin to tell you why it is and why if you are a scuba diver you should probably wear one, first let me explain what a dive watch is.  There are many “dive style” watches that look the part but are not.  To really be considered a dive watch there is a series of standards (ISO 6425) a timepiece must meet including 100 meters of water resistance, a timing device (such as a unidirectional bezel) protected against inadvertent rotation, a certain quality of illuminated markers in dark conditions, etc. Before the advent of dive computers, a watch that could survive the water pressure, track the elapsed time of a dive and/or a decompression stop, and be read in low light, was an absolutely essential survival tool.  It, combined with decompression tables, some good old-fashioned math skills, a submersible pressure gauge and an analog depth gauge (which tracks both current and maximum depth) served the same purpose as a modern dive computer.  I find it somewhat ironic that most diving kits include an analog console with submersible pressure gauge and depth gauge but exclude an analog timing device.  Now before anyone gets in a techno-huff, I absolutely believe in using a dive computer and I own two of them, the professional Shearwater Perdix with wireless Air Integration and the more recreationally oriented and smaller Atmos Mission One (so no scuba luddite am I).  However, I also wear a dive watch while diving (and usually out of the water) and I think new students should be trained to use dive tables and analog gauges as well as computers.

In general, I think the Open Water course is too short and has grown ever lighter on some all-important theory and technical aspects (the boring stuff) (also the stuff that keeps you safe, alive, and uninjured).  I think it is very difficult to really understand what a computer is actually doing and telling you without learning the process the older way.  This is true for many things, such as the exposure triangle in photography and starting a fire in the wild.  The U.S. military has had problems when land navigation (map and compass skills) are no longer taught because everyone has high-tech GPS abilities.  GPS is incredible until batteries die, a system is hacked or goes down, electronics fail in austere environments or, well, it’s just wrong.  Then it is a very good thing to know how to use a paper map and a good old-fashioned battery-free compass (and also a watch unattached to any system other than your wrist).

I freely admit that while not being a luddite, I am a traditionalist.  I love watches, in particular dive watches, and I think they have a Romance about them that echoes the early days of scuba diving, the adventures of Jacques Cousteau, frogman commandoes, and Mr. Bond himself.  I think this is why they are perhaps the single most popular style of watch, even though relatively very few are owned by actual divers and even fewer are ever taken underwater.  You may never become a certified diver, you may never wear your dive watch under the waves, but just the presence of it on your wrist gives you hope through long days at the office where there are never any undersea knife fights or octopus attacks, and you never seem to catch a glimpse of Ursula Andress emerging from the Caribbean in a white bikini.  So, I will also freely admit that one reason I wear a dive watch is that seeing it underwater, strapped over a wetsuit opposite my fully modern computer, gives me a lot of joy.  It makes me happy knowing that my watch, of all its brothers and sisters out there, got lucky enough to be used as designed.  But I digress…

First and foremost, the dive watch is useful as a backup.  If you set the timing bezel before entering the water it provides a reliable, ever-present count, of how long you have been submerged.  You look at the watch, a device that both shows you the time and reminds you of its passage, and you can tell at an instant how many minutes you have been underwater.  A dive computer gives you all sorts of valuable information, most certainly including elapsed time, but a watch basically just does that one, all-important thing.  And to me anyway, its very presence reminds me to be aware of time (and then depth, and then air-pressure)… to remember my status as a visitor in the underwater realm and the fragility of my existence there.

I also found it very useful during my recent Rescue Diver course where I had to run a search pattern based on time and depth.  We were looking for a “lost diver” or in this case we were actually looking for a real lost object (a weight pouch someone had dropped a few weeks earlier).  One of the Instructors knew roughly where it had been dropped: somewhere on a fairly steep, muddy slope rising from the depths up to the rocky shore.  So, I began the search at a certain depth, and we followed that depth (using the computer reading) for three minutes.  Then we would ascend about 10 feet and swim the opposite direction for three minutes.  I found, in this case, that tracking time using my watch’s second hand was easier than using the computer.  So, I concentrated on the depth readout number on one wrist and the time passing on the other and… we found the missing weight pouch.

So, is a dive watch the mandatory piece of kit as it used to be?  Well, no, it is not.  I do believe, however, that it functions as both a useful backup and a practical tool, in its own right.  Used correctly, it can make you a better, safer diver and let’s face it, it looks a lot cooler than wearing a computer on your wrist, especially while telling tall tales after the diving is over.  Best to leave the computer to fully dry off and charge for the next day’s diving.  You can leave it to your watch to tell you when it is time to go to bed as you regale the palm-thatched bar with stories of mutant sharks, near-escapes from giant squids, and the increasingly uncommon underwater knife duels with agents of shadowy international criminal organizations.