PLAN the dive, DIVE the plan.
One of the weakest critical skills that novice technical divers possess is the ability to PRECISELY follow a plan. Run-Time precision. For that reason, pre-cut tables stress the need to maintain situational awareness, plan ahead in-water and get your ascent profile exactly right.... RUN TIME matters.
Computers discourage the importance of run-time adherence... everything is recalculated on a dime, things get sloppy.
IMHO, run-time precision is one of the fundamental tech competencies. Whilst tech divers may go on to utilize computers, they should have their foundations cultivated first.
There's nothing "old school" about it. Any more than practicing accurate buoyancy is old school... or learning frog-kick, or rehearsing gas switches
So.... a recreational diver buys a Petrel. They use that Petrel to formulate a precise dive plan. Once in-water, the Petrel deviates from that plan, due to depth fluctuations etc etc. Stop times, or even depths, can differ. Allowable bottom time can differ. Which plan does the recreational diver now use? The original plan; run-time and stops? Or the current plan presented by the Petrel?
My money is on people using the current in-water directions from the computer. Bravo! They've learned that deviation from pre-dive plan is acceptable. That discipline is a dispensable factor.
Weeks, months or years later... they turn up at a technical diving course and struggle with the concept of following accurate run-times. I see this far too routinely and more frequently as the current generation of 'trained only on computers' divers reaches tech level.
Scubaboard is full of comments about how this or that computer is too conservative, too restrictive etc etc
How about having the flexibility to drop VPM down to conservatism zero.... as is default on most rec computers. How about GF Hi 100?
I don't assume any decompression theory knowledge... no algorithm clarity... with recreational divers... so the computer happily allows you to set conditions and parameters that decrease your safety. Recreational divers might easily assume that anything you are 'allowed' to set, must be safe. That's how other computers work right?
Shearwater themselves caveat and disclaimer against this boldly in their instruction manual. They direct towards the user educating themselves. It's the only computer instruction manual that tells users to read Baker's "Understanding M Values" article...
You know as well as I do that assuming the software you cut the table with and the computer are running the same algorithm, that diving a square profile plan with a computer will almost always leave the computer clearing the stops slight before your run time plan as the actual dive rounds off the square corners on the plan.
Thus, the diver dives the plan, and the computer runs in the back ground as backup. What does that teach the diver? It teaches the diver to think, and to dive the plan - and it teaches him that rigid reliance on the computer isn't always needed, but also that the computer will usually run pretty close to the dive plan, and is a reasonable backup.
In the real world however, there are times when diving the plan isn't the best option. Let's say you're only half way through your bottom time, and you discover that due to high current, you're burning more gas than planned (which is one of the key reasons to have a dive and gas plan), or lets say you're on the plan and you arrive back at the hook to find it's gone, and you have to shoot your own ascent line, or let's say you encounter another diver with an emergency and you need to get them to the surface or at least to surface support ASAP, or perhaps there is just a recall signal from the boat due to sea conditions brewing up, an injured diver, etc. That's where a computer comes into it's own. If you're at 200' and only 15 minutes into a 30 minute bottom time, it's nice to have a computer that can get you to the surface safely and in minimum time - particularly if you're dealing with some other unexpected crisis or failure. At that point the computer is a much better option than doing the full deco schedule (and probably on-gassing rather than off gassing at the deep stops), or perhaps putting a new deco schedule together with wet tables while hanging on a jon line at depth in a 3 kt current.
Or consider the reality of diving in a cave, particularly one with an unknown profile. In that environment, the gas plan is based on a minimum of thirds, with adjustments for flow, silt and line conditions, tight passages, and deco obligations. Absent a computer, you're reduced to developing a multi-level dive plan on the fly, when your focus is better spent on a variety of other items. Or, you force yourself to comply with a square deco profile, which again wastes significant time on in needed deco.
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Your point is well taken that a diver can change the default GFs in a Shearwater, but let's be honest here and point out that changing the conservatism or the GFs is an option in most dive plan software as well. In both cases, the diver needs to understand the theory behind it before they start adjusting GFs. You can also get a VPM-B unlock for the Predators which gives it the flexibility to match deco planning software using GFs or a variable permeability model.
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In short, you're making an argument that a computer causes bad divers, rather than recognizing that a computer is just a tool, and that the diver is responsible for all the planning and decision making - a philosophy that is built into Shearwater computers.
