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The modified values of <math>a</math> and <math>b</math> are shown in bold in the table below.
===Helium (heliox) set of parameters===
According to Graham's Law, the speed of diffusion (or effusion) of two gases under the same conditions of temperature and pressure is inversely proportional to the square root of their molar mass (28.0184 g/mol for N<sub>2</sub> and 4.0026 g/mol for He, i.e. <math>\sqrt[2]{\frac{28.0184}{4.0026}}=2.645</math>), which means that He atoms diffuse 2.645 times faster than N<sub>2</sub> molecules.
Bühlmann took this into account and divided all the tissue compartment half-time for air (nitrogen) by 2.645 to obtain a helium-specific set of parameters with the longest compartment set at <math>\frac{635}{2.645}=240\text{ min.}</math>
The parameters of the M-Values (coefficients ''a'' and ''b'') were determined specifically.
===Trimix (nitrogen + helium) set of parameters===
No model can manage the de-saturation of two inert gases.
Some approaches only take into account the main inert gas (and ignore the other inert gas).
With Bühlmann,<ref name="Buhlmann-trimix" /> a weighted average of the half-times and coefficients <math>a</math> and <math>b</math> is calculated as a function of the percentage of each inert gas to calculate a specific set of parameters.
;Numerical example with trimix 18/50
Using a 18/50 trimix (18% O<sub>2</sub>, 50% He, 32% N<sub>2</sub>), the half-time (or the ''a'' and ''b'' coefficients) of compartment #1 is calculated by taking 50% of the He half-time and 32% of the N<sub>2</sub> half-time divided by 50% + 32% = 82%.
<math>t_{1/2}= \frac{(1.51 \times 0.5)+ (4 \times 0.32)}{0.50 + 0.32}=\frac{(0.755 + 1.28)}{0.82}=2.48 </math> (instead of 1.51 with He and 4 with N<sub>2</sub>)
<math>a = \frac{(1.7424 \times 0.5)+ (1.2599 \times 0.32)}{0.50 + 0.32}=\frac{(0.871 + 0.403)}{0.82}=1.5541 </math> (1.7424 with He and 1.2599 with N<sub>2</sub>)
<math>b = \frac{(0.4245 \times 0.5)+ (0.5050 \times 0.32)}{0.50 + 0.32}=\frac{(0.2122 + 0.1616)}{0.82}=0.4559 </math> (0.4245 with He and 0.5050 with N<sub>2</sub>)
The same calculations can be made using partial pressures rather than percentages.
This approach is controversial with some authors<ref name="Salm-1" /> who feel that this calculation does not reflect what should be achieved. Generally speaking, the fact that desaturation with two neutral gases is not modelled encourages caution. Each trimix dive is specific, with no guarantee.
=== Constant partial pressure of oxygen PpO<sub>2</sub> (closed-circuit rebreathers - CCR) ===
There are no specific model for constant PpO<sub>2</sub> dives. The difference lies in the fact that, at all times, the proportion of inert gas is calculated in relation to the chosen PpO<sub>2</sub> (e.g. 0.75 or 1.3 ata (bar)).{{clarify}}
===Versions===
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