Anyone who has aspirated water should see a physician. We can not see some of the effects that water aspiration may have caused and only a trained medical physician can clear someone after such an event.
Check out your PADI Encyclopedia for loads of great information about cylinder materials, capacity and weight/displacement details to help refine both your and your divers' techniques and to expand your own diving knowledge.
The (+) appears on the neck of steel cylinders and denotes their overfill capacity.
Time to break out your Greek skills again. Hypercapnia means more than a normal amount of Carbon Dioxide.
Each compartment has 6 halftimes. If the halftime for this compartment is 60 minutes that means it will take 60 minutes for it to become 50% saturated.
It will then take another 60 minutes to fill 50% of the remaining space within the compartment.
This means it will be 75% saturated as two halftimes have elapsed and taken 120 minutes to do so.
Remember that partial pressure refers to the physiological effect rather than the physical amount.
Take the percentage of gas in the breathing mix and turn it into a percentage (21% O2 = 0.21 ppO2)
Then multiply it by the ambient pressure of the gas when the diver breathes it. at 26 m/sw that's 3.6 ATA. (0.21 X 3.6 = 0.756).
Rounded to two decimal places you'll get the right answer.