Bubbletrouble, this is getting pretty far off topic here, so pretty soon we will need to agree to disagree, but I feel compelled to reply to your comments.
I think you've completely discounted the ability/quality of the instructor in your analysis of which classes are "important to take."
Not all classes or content is created equal. There are some courses which it is important to take, and some which are not. The purpose of taking a course is to gain additional knowledge and skill so as to make ones diving safer. It does not follow that every diving activity requires a course. I would say it is fairly common to dive off a boat, but would submit that most, if not by far the majority, of divers who dive off a boat have never taken the boat diver specialty course.
Let me preface what I'm going to say by stating that I'm not an experienced altitude diver.
This is my issue with your statements in this thread, you are somewhat out of your element, but compensate by being vague. You started by saying you wouldn't buy a computer, but then never told us what piece of gear you would buy, then you jumped on my suggestion that if the diver was diving locally, they should buy equipment that would facilitate that. I think what you were trying to say in the above quote was that you had NO experience with altitude diving, but feel free to correct me here, I'm just reading between the lines.
If I planned to conduct dives at altitude, I would take an approach that any thoughtful person would. I'd seek out the knowledge to do that kind of diving safely -- whether that be in the form of a formal class (with a competent teacher), reading materials, or direct mentoring with an experienced altitude diver. FWIW, I'd feel most comfortable using a combination of all three methods of education and asking lots of questions of my mentor/other experienced divers. I would also read articles in the scientific literature which discussed real/potential risks of altitude diving.
I think we can agree here, when deciding to do any new diving it is imperative one understand the specific risks, and how to mitigate those risks to what extent is possible, but that may not be in a "formal" course. I submit that it depends on how much knowledge you need to acquire, and the skill differences from the type of diving you are experienced with. Those of us who were trained in these environments do not need to take additional courses to "certify" what we already know, that is called badge collecting.
If you did the research, I think you would find that the difficult part of altitude diving is not the altitude in and of itself; its the water temps, its the additional gear, and the task loading associated with operating that gear, it can be visability, but the altitude itself merely changes the values and risks associated with concepts already covered by any decent ow course.
While purchasing a computer that adjusts NDL calculations automatically for high altitude diving might be a nice convenience, it certainly shouldn't be relied upon as the sole tool for safe altitude diving. Manufacturers will implement functionality in their dive computers in various ways.
Obviously it goes without saying that one needs to know how to operate their computer and what the gear does and does not do. That goes for any gear, in any type of diving. You understand that each manufacturer has their own implementation of one of various decompression algorithims? Some computers are more conservative than others and also some have more bells and whistles while some do not. This goes for all diving, not altitude diving in particular.
In so far as using the computer to calculate the ndl for the diver, you should realize that several certification agencies are dropping the tables from their course requirements altogether. I know for a fact that SSI has done this with OW, and PADI and SDI have for nitrox. We can debate the wisdom of this, but that is a separate thread altogether.
In addition, computers will correct for the density difference between sea water and fresh water. Analog depth guages are calibrated for sea water and will not read correctly in fresh water. Thanks, but I will take the computer over an analog depth guage and tables.
Then there's the logistical concern of what a diver does immediately after his altitude dives. In some mountainous regions (the same ones that offer opportunities for diving), divers have to navigate mountain passes with significant elevation changes on their way home after a day of diving.
Obviously this is unique to the individual geography of any area, but at least in this area, the dive sites are typically the highest points of elevation a diver would typically go to during a typical dive day. Also, keep in mind that the pressure changes in air are significantly less than the pressure changes in water. Altitude increases of less than a few hundred feet should not pose a significant hazard when using standard recreational dive profiles. Most often, speaking of the local areas for the OP, one would be staying near dive altitude or descending, thus negating any special considerations for normal recreational dives. Although again, I do not see this as a special consideration for altitude diving. For me, if I drive to the pacific northwest for ocean diving, I need to drive back across the rocky moutains to get home. I need to consider the time and altitudes even though I am NOT altitude diving.
I think, with altitude diving in particular, it would be a good idea to brush up on dive emergency preparedness (rescue class, oxygen provider, CPR, etc.). As you know, even if a diver conducts dives within the allowable limits of his computer, it's possible to get bent.
This goes for all diving, and is not particular to altitude diving.
I wouldn't be surprised if the safety margin afforded by common deco algorithms is even slimmer with altitude diving (vs. diving at sea level and taking into account the added conservatism adjustments).
I'm not sure how one would know this, I would suppose that it would be like any other ndl calculation, it would depend on the individual manufacturer and their implementation of the chosen decompression algorithm.
Several of the currently offered Suunto computers do not automatically adjust to diving at altitude. The user has to manually select the proper mode A0, A1, or A2 in order for the NDL calculations to add conservatism adjustments to the modified RGBM algorithm.
If you re-read the posts, you would see that we have been discussing the merits of using a computer for altitude diving. The computers do in fact have altitude adjustments, and will automatically calculate the ndl for the divers at the altitude selected. Each computer will have its own implementation, which goes back to knowing how your gear works.
). In fact I specifically decided to get the computer so I would not have to manually adjust for altitude.
