Mr Chen, I set the oxygen partial pressure to 1.4 b which is conservative for recreational diving and typically use a 32% oxygen mix. On a recent dive trip I did get close to the NDL but we were doing multiple dives a day and the dives were relatively deep. Generally it wasn't a problem and having this mix made a big difference in the time I could spend at depth without getting close to the NDL. Not surprising since that is why you use Nitrox. :blinking: With a 32 % oxygen blend I can get down to 33 m. In this case the simple solution for me was not to exceed 33m. If I ever did want/need to go deeper I'd probably just go with straight air.