Editing Maximum operating depth (section)

==Formula==
The formula simply divides the absolute partial pressure of oxygen which can be tolerated (expressed in [[Atmosphere (unit)|atm]] or [[Bar (unit)|bar]]) by the fraction of oxygen in the breathing gas, to calculate the absolute pressure at which the mix can be breathed. (for example, 50% nitrox can be breathed at twice the pressure of 100% oxygen, so divide by 0.5, etc.). Of this total pressure which can be tolerated by the diver, 1 atmosphere is due to surface pressure of the Earth's air, and the rest is [[Hydrostatic pressure|due to the depth in water]]. So the 1 atmosphere or bar contributed by the air is subtracted to give the pressure due to the depth of water. The pressure produced by depth in water, is converted to pressure in [[feet sea water]] (fsw) or [[metres sea water]] (msw) by multiplying with the appropriate conversion factor, 33&nbsp;fsw per atm, or 10 msw per bar. 

'''In feet'''

<math>MOD (fsw) = 33\mathrm{~fsw/atm} \times    \left [\left ({pO_2\mathrm{~ata}\over FO_2} \right ) - 1\right ]</math>

In which pO<sub>2</sub> is the chosen maximum partial pressure of oxygen in atmospheres absolute and the FO<sub>2</sub> is the fraction of oxygen in the mixture. For example, if a gas contains 36% oxygen (FO<sub>2</sub> = 0.36) and the limiting maximum pO<sub>2</sub> is chosen at 1.4 atmospheres absolute, the MOD in feet of seawater (fsw){{refn|group=Notes|[[Feet sea water]] (fsw) is a unit of pressure. One fsw is equal to the hydrostatic pressure exerted by a standard sea water column of 1 foot height at normal Earth gravity. 33&nbsp;fsw is approximately equal to one standard atmosphere (atm). A pressure indicated in fsw is gauge pressure (relative to surface pressure) unless specified.}}  is 33&nbsp;fsw/atm x [(1.4&nbsp;ata / 0.36) − 1] = 95.3&nbsp;fsw.<ref name=NOAA />

'''In metres'''

<math>MOD (msw) =10\mathrm{~ msw/bar} \times    \left [\left ({pO_2\mathrm{~ bar}\over FO_2} \right ) - 1\right ]</math>

In which pO<sub>2</sub> is the chosen maximum partial pressure in oxygen in bar and the FO<sub>2</sub> is the fraction of oxygen in the mixture. For example, if a gas contains 36% oxygen and the maximum pO<sub>2</sub> is 1.4 bar, the MOD (msw) is 10&nbsp;msw/bar x [(1.4&nbsp;bar / 0.36) − 1] = 28.9&nbsp;msw.