It’s essential that the Dive Supervisor can rapidly calculate the percentage of oxygen to add to an air bank to get the desired Nitrox mix.

The good thing is that there is a rapid solution to calculating this.

This is the Nitrox Triangle.

You want to make a 32/68 Nitrox mix. You have an air quad containing 180 bar. 

You have to decant how many bars of 100% O2 to obtain the 32/68 mix and what will be the pressure in the Quad when obtaining the 32% O2 ?

180  ÷  68   x   11 = 29.1 bar

Add 180 bar to 29.1 = 209.1 bar 

Check 180 ÷ 68 x 79 = 209.1 bar

Therefore, you need to decant 29.1 bar of 100% oxygen to have 209.1 bar on 32/66