Things Scuba Instructors teach that are either bad or just wrong.

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I back the knob a bit on my tank, don't give a crap about Nitrox, face my spg away from me, occasionally touch the bottom, VIP my own tanks, often have my mask on my forehead at the surface and don't usually carry a snorkel.

The horror...the horror...

Unclean! Unclean!

🤣
 
If scuba instructors teach from a book then we could be in trouble with this. From SSI's science of diving course book (copyright 2010) under the section on dive computers from the chapter on decompression theory we have this:

"Going deep, then shallow, then deep again will yield unreliable results. Since a dive computer is an actual computer, an old axiom in the computer business is applicable here: 'garbage in equals garbage out.' .......if a diver dives improperly the computer will calculate improperly."

What's the lesson? Don't do reverse dive profiles because that is improper diving and your computer won't be reliable.
 
Twice I have seen people get smacked in the face by the face plate when they opened the valve even though they were told to turn it away and turn the wheel/handle slowly. Not all SPGs have the plug in the back.

It is not unheard of for teachers, instructors, professors to pass on misinformation because they haven’t questioned or verified their knowledge. In most cases people simply don’t know what the don’t know.
 
So I would never use Nitrox when not needed, exactly as I do not use any drug if not strictly necessary.
Moderation in all things, including moderation
 
said to hold the 2nd stage purge button down when turning on tank air
That's actually to protect the hp seat in the first stage. The knife edge on the seat is small, and when 3kpsi hits, it can leave a mark. In the old days it was not too unusual to see a seat crack on first turn on. That would be before the turn of the century. The last one that popped on me was early 2000s. It certainly got my attention as the tank was on my back when the knob was turned on. Those brown stains did not come out.
 
I actually can relate a couple stories of things I was taught as a student that were just plain wrong and had agency approval. The following examples all come from my early tech training.
  • I was taught that altitude was not a factor that needed to be considered in planning ascents. My instructor taught me this, and the owner of the agency supported him thoroughly. When I asked the owner how he knew, he said he did decompression dives at Lake Tahoe using the same ascent plan he used at sea level, and he was fine. Therefore, altitude is not a factor.
  • I was taught that on ascent, when I switched to 50% oxygen, I needed to do the first couple stops (70 feet and 60 feet) for longer times than the next couple of stops. This was called an S-curve. It is the opposite of normal ascent strategies. Anyone with any real authority would say that is just plain wrong. I thought it was just plain wrong, but as a student, I had to do it that way.
  • When I reviewed the official academic material on decompression theory, I thought a lot of it was wrong. I asked my instructor about it, and he said that if I didn't like it, I should leave the program. I asked the owner of the agency (the author of the materials) about my concerns, and he at least responded with explanations. We went back and forth on it for a while, and then there was an agency-wide announcement that we should stop using those materials, as they were being rewritten.
 
You don't need a class, you can learn everything you need to know on internet forums.
 
https://www.shearwater.com/products/perdix-ai/

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