Dive computer

A dive computer is a scuba diving gadget which constantly displays the amount of time that a diver can continue to stay underwater before he or she has to surface for his own safety in order to avoid getting decompression sickness, or "the bends".

Inside the watertight case, a battery-powered electronic computer uses a depth gauge and clock to track the depth profile as it regularly samples the current water pressure, and uses this information to estimate the current depth and the amount of nitrogen that has been dissolved in the diver's blood. An LCD display on the face of the dive computer shows the number of minutes that the diver is allowed to remain underwater at his current depth before he or she has exceeded safety recommendations. As time passes and the diver ascends and descends in the water, the display changes accordingly.

Dive computers also display the current depth, the amount of time the diver has been underwater, and the maximum depth reached during the current dive, so the diver can keep true to his original dive plan and surface after the agreed-upon dive duration. Most dive computers keep track of this information for at least the last ten dives so the diver can later write this information down in his diver's log book.

Other available dive computer features include:

• Temperature gauge
• Display of the speed of ascent, with warnings
• Audible alarms
• Air pressure gauge to display how much air is left in the tank
• Connection to a personal computer for detailed log purposes
• Nitrox as well as normal air compatibility
• "Time to Fly" display showing when the diver can safely board an airplane

Most can be inserted into normal air and depth pressure gauge fittings, or onto a wrist mount. Many computers go into a "lockout" if the diver violates the safety limits, to discourage continued diving after an unsafe dive. While in lockout mode, these computers display depth and time only, while flashing various warning signs telling the diver that he or she should surface. After a lockout, many computers remain locked out for 24 hours.

Scuba instructors recommend that divers follow the limits of the dive tables they receive as part of their training, forming a dive plan and then following it -- this as opposed to simply jumping into the water, dropping down, and keeping an eye on their dive computer until it says that it's time to surface. Following a dive plan is good procedure and will help protect divers if they lose their dive computer in the water, or if it runs out of batteries or even if its software crashes.

Different brands and models of dive computers are called more "conservative" or "liberal", where "conservative" means the computer limits diving time more in order to increase the margin of safety against decompression sickness. Experienced divers may want to use a more "liberal" computer, but this may increase risk. Complicating this choice is the fact that susceptibility to decompression sickness is not well understood, and it seems to vary depending on the diver's fitness, age, weight, fatigue, and even recent illness, as well as the water temperature and the altitude.