Its essential that the Life Support Tech can rapidly calculate changes to  to depth, ppO₂ or percentage of oxygen in heliox.

The good thing is that there is a rapid solution to calculating one of these elements if you have two of the other values.

To calculate depth:

Depth = ppO2  x 100 ÷ %

ppO2 = 0∙400 bar

% = 6.6 

Depth = (0∙400 x 100 = 40) ÷ 6.6

Depth = 40 ÷ 6.6 = AP 6.06 x 10  = 60.6 – 10 m  = 50.6 msw 

Depth = 50.6 msw (Rounded to 50 msw) 

50 msw

To Calculate ppO₂

ppO2 = Absolute Pressure (AP) x % ÷ 100

(AP) = 55 ÷ 10 +1 = 6.5

ppO2 = 6.5 x (9.23 ÷ 100  =  0.0923)

ppO2 = 6.5 x 0.0923 = 0.599 bar = 599 mbar (rounded to 600 mbar)

600 mbar

To calculate O₂ percentage

% = ppO2  x 100 ÷ AP

ppO2 = 0.375 bar

(AP) = 75 ÷ 10 + 1 = 8.5

% = (0.375 x 100 = 37.5) ÷ 8.5

% = 37.5 ÷ 8.5 = 4.4

% = 4.4

4.4%

• IMCA D022. Guidance for Diving Supervisors Manual, Chapter 2, Section 7