Dive tables and PADI exam

We completed the theory component of our Open Water course this afternoon, with a final class (held by Lucy, another one of the instructors) teaching us about the use of dive tables. When you go diving, your body absorbs a higher-than-usual amount of nitrogen (depending on depth and time); and dive tables are used to calculate how much nitrogen you've absorbed (approximately), and to help you keep within safe nitrogen level limits. Lots of theory about such things as: pressure groups; nitrogen quantity; minimum surface intervals; and total bottom times. Once the class was done, we'd been taught all the required theory for the course, and so we were ready to undertake the final exam.

The teaching of the theory component of the course may have been something of a joke: but the PADI final exam was a complete joke. We were told to all complete it downstairs, in the restaurant; we were encouraged to talk to each other, and even to blatantly copy off each other; and at the end of the exam, rather than being passed or failed, we simply signed a statement saying: "any questions that I answered incorrectly have been explained to me, and I now understand them". It was multiple-choice, and I scraped in a solid 47/50.

Using dive tables involves a little bit of maths, but it's pretty simple stuff. Basically, it's just a lot of lookups, and a bit of addition as well. Why, then, did my head hurt so much when I was doing the calculations, and why did I find it all so inexplicably difficult? I guess that since I've done nothing more complex than restaurant maths over the past year, and that since my maths has never been terribly crash-hot, my brain's arithmetic muscles have all but shrivelled up and died. Has a year-long holiday made me braindead? I hope not, because in one month's time I'm going back to university, and beginning an intensive thesis program! Perhaps I should tickle my brain a bit, before I dive back into the studying life.