Here's one of the important things I must remember: because the air pressure at sea level is one atmosphere (14.7 PSI), you have to remember to add a one every time you descend another atmosphere. So 33 feet is 2 atm, and 66 feet is three. You divide the number by 33 for saltwater (34 for fresh), and then add the one to get the number of atmospheres.
I also need to remember that the weight of 1 ft.³ of salt water is 64 pounds. And for freshwater, it's 62.4 pounds. Also, water moves heat away from the body 20 times faster than air. And sound travels 4 times faster in water than air, because water molecules are more dense and elastic than air. That makes it difficult to determine from which direction the sound is coming… And often makes a sound appeared to be coming from overhead.
Thanks to Chris for this! ;)
And let's hope this is my reaction after the exam. Can't wait to break into the bottle of champagne I've got chilling in the fridge!