Rainer
Contributor
Ah, now I recognise this as a modified rule of 120/140. It kind of slides between air (120) and 32 (140). Are these used with depth averaging?
For those who don't know, a quick way to check your dive plan against reality is to use the rule of 120/140. Subtract the depth from 120 for air and 140 for NitrOx and you have a gross approximation of what your NDL should be. For a dive to a depth of 60 ft
120-60 = 60 min on air
140-60 = 80 min on NitrOx
These were never meant to replace tables or a PDC and they don't rely on depth averaging. I also recommend a full five-minute safety stop in any event.
Around the GUE divers I knew (myself included) we always used a 130 (not 140) rule for 32% (with conservative depth averaging). I probably have 800 recreational dives using that method without issue.