What is the 120 rule in scuba diving?
Miriam Grasso
2025-05-24 03:07:37
Numero di risposte: 7
You will sometime hear divers refer to the Rule of 120.
The "Rule of 120" was based on the sum of depth and NDL, which turned out to be 120 for the old Navy tables, exact between 60 and 90 ft.
It was for the first dive, only.
You who are mathematically inclined will recognize this as a tangent-linear approximation to the deco curve.
This same "Rule of XXX" could be applied to pretty much any dive table or dive computer, for the first dive.
Find that depth at which the sum of depth and time is the minimum, and that is your new rule.
For air, here are some other "Rules;" remember, your depth must be in feet for these to be valid.
It gives a quick estimate of your NDL without looking at a table or plan mode on your computer.
I just remember 115 for 31%.
NDL for 80 ft is thus 35 mins, with more conservatism deeper and shallower.