Quote Originally Posted by ScubaStingRay View Post
I'm not sure, but from what I researched it could be because you don't have a doubles endorsement of your card? If you didn't have it they might just post about the 1/3 of singles rule and not mention doubles. I read a bunch of older threads, and it seems like you need to request the endorsement otherwise it can be left off.

Someone with more knowledge please correct me.
TDI doesn't have a "double's endorsement" for Intro to Cave. I received my Intro training with Rich in 2012, all in sidemount, and I was trained that my turn pressure was 1/6th total gas supply when diving doubles (BM or SM). However, the older TDI Intro cards read: "Max depth 130 ft w/30 ft., no deco dives, no restrictions, reserve 2/3 air supply to exit, continuous guideline to exit, at least (3) batter powered lights per diver." So I can see where some people consider this a license to dive to thirds....
I believe that TDI has since corrected this, as the new cards state: "Penetration limited to 1/3 single cylinder or 1/6 doubles. Max depth 40M/130FT. No Deco. No restrictions. Maintain single continuous guideline to exit"
None of this is because the rules have changed, this is all because divers were using the single tank gas limits and applying it to doubles--and some instructors may have allowed this (I know mine did not).