When North American divers arrives at foreign dive resorts, they can become confused about tank size . After all, we use the Imperial system and our tanks are measured in cubic feet.

Much of the rest of the world uses the metric system, about which most Americans are embarrassingly ignorant, so when we see a tank size measured in liters, we get perplexed . To complicate matters, the Imperial system uses psi, while the metric system uses bar. One bar is close enough to 14 .7 psi, so we Imperialists don't have to worry about the difference.

However, liters and cubic feet are not interchangeable when it comes to tank sizes, because it is the manner in which the tank size is expressed . Liters describes the size of any empty tank before it is filled, while cubic feet describes the amount of gas in a full tank.

But at least remember this: If you're standing at a dive dock and given the choice of a 105 cu . ft . tank with 3000 psi, or a 15-liter tank filled to 200 bar, you can take either because they'll deliver just about the same amount of air.

Or, suppose you pick an aluminum 80 filled to 3000 psi, and you dive with a buddy sporting a 11-liter tank filled to 207 bar, if you breathe at the same rate, you'll be coming up together.

Forward this article to your dive buddy