Any decent Instructor will agree to this AND show you how to set your computer aswell..Otherwise what possible reason could they give for not teaching it???
I'm guessing if they sell a course of 'X' content, based on 'Y' duration, for 'Z' cost... then they would have a legitimate reason for not supplementing time/effort/material into that course for no financial reward.
Let's face it... the PADI Nitrox course is
very basic in scope... but it's also
very cheap.
Not saying I agree with that... just that it's understandable. Especially if that material is available in subsequent courses (it is), that you'd have to pay for.
There's very few scenarios where a recreational diver would have to be too concerned about OTUs and CNS%. It's primarily a concern for technical divers doing accelerated decompression on rich O2. That's why it's typically taught on entry-level tech. Courses
do tend to teach you what you need to know at
that level, rather than pre-empting future levels.
What the formula or table to calculate the time at which a particular cns level will degrade over time?
These are given in tables. PADI supply those on the Tec40 course. Other agencies supply at the equivalent level: Advanced Nitrox.
Like these:
CNS Exposure Table
and here:
Diving with Nitrox
If you want a true recreational course that teaches in-depth nitrox use, then look to the ANDI Complete SafeAir User (CSU) course. It's very comprehensive.