Professional divers use such a calculation only as a rough guide to give new divers a metaphor, comparing a situation they may be more familiar with.Reported signs and symptoms are summarized against typical depths in meters and feet of sea water in the following table, closely adapted from Deeper into Diving by Lippman and Mitchell:

Causes
The cause of narcosis is related to the increased solubility of gases in body tissues, as a result of the elevated pressures at depth (Henrys law). Modern theories have suggested that inert gases dissolving in the lipid bilayer of cell membranes cause narcosis. More recently, researchers have been looking at neurotransmitter receptor protein mechanisms as a possible cause of narcosis. The breathing gas mix entering the divers lungs will have the same pressure as the surrounding water, known as the ambient pressure. After any change of depth, the pressure of gases in the blood passing through the brain catches up with ambient pressure within a minute or two, which results in a delayed narcotic effect after descending to a new depth. Rapid compression potentiates narcosis owing to carbon dioxide retention.A divers cognition may be affected on dives as shallow as 10 m (33 ft), but the changes are not usually noticeable.
For example, hydrogen at a given pressure has a narcotic effect equivalent to nitrogen at 0.55 times that pressure, so in principle it should be usable at more than twice the depth. Argon, however, has 2.33 times the narcotic effect of nitrogen, and is a poor choice as a breathing gas for diving (it is used as a drysuit inflation gas, owing to its low thermal conductivity). Some gases have other dangerous effects when breathed at pressure; for example, high-pressure oxygen can lead to oxygen toxicity. Although helium is the least intoxicating of the breathing gases, at greater depths it can cause high pressure nervous syndrome, a still mysterious but apparently unrelated phenomenon. Inert gas narcosis is only one factor influencing the choice of gas mixture; the risks of decompression sickness and oxygen toxicity, cost, and other factors are also important.Because of similar and additive effects, divers should avoid sedating medications and drugs, such as cannabis and alcohol before any dive. A hangover, combined with the reduced physical capacity that goes with it, makes nitrogen narcosis more likely. Experts recommend total abstinence from alcohol for at least 12 hours before diving, and longer for other drugs. Prognosis and epidemiology
Narcosis is potentially one of the most dangerous conditions to affect the scuba diver below about 30 m (100 ft). Except for occasional amnesia of events at depth, the effects of narcosis are entirely removed on ascent and therefore pose no problem in themselves, even for repeated, chronic or acute exposure.