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If one get certifed in scuba diving does it apply in free diving and visa versa?
Does the same concept apply in both?
Short answer to "vice versa" and "the same concept" is "no"
I've never encountered a scuba dive operator who required any certs at all for free diving (or snorkeling).
Are you interested in getting training in one or the other? Some agencies (SDI, for example) offer extensive freediving training as well as scuba diver training.
My uneducated guess is that back then people interested in scuba had already learned proper swimming and done a fair bit of snorkeling. Different world now.Years ago, when the YMCA was involved in diver training, they offered (and recommended) a skin diver (free or snorkel) course, as a prerequisite to their scuba course. Many of the water skills are useful to both activities, and the Y's emphasis on continual training and developing core competencies began with how to use a mask, fins, snorkel and safety vest before progressing to a tank, regulator and bcd. For those of us who went through the program, it was well worth it and made us more confident in our abilities under water before starting scuba training.