I use a 19 cft pony when diving solo or deeper than 100' (max 130'), my question to the Tech Divers is what percent nitrox mix should I use. My present mix is 40%, I know it exceeds the 1.4 or 1.6 ppo but my reasoning is that in an emergency I would be using this mixture for a short period of time, basically from a max of 130' to 70' my exposure time would be two to three minutes, also at the 15' safty stop I could switch from my dive gas to the pony bottle with the 40% nitrox to increase safety margins for NDC limits.