A dive computer (also known as a deco meter, decompression meter, decompression computer, and/or scuba diving computer) is an absolutely essential component of a scuba diver's gear. The dive computer functions to track your depth in the water and time spent underwater. Then by using algorithms which simulate the current diving conditions, the dive computer displays the safe time and depth to stay within. Monitoring a diver's depth and time underwater will keep nitrogen levels in the body below a dangerous threshold (beyond which a diver might experience decompression sickness caused by the rapid increase in nitrogen's capacity to dissolve in the body as the diver goes deeper, due to the increase in pressure).
Dive computers come in two basic interfaces: independent, and integrated. Independent dive computers are not connected to your other equipment, and are typically worn on the wrist or are placed in an instrument console. Integrated dive computers are connected to your submersible pressure gauge, and sometimes other electronic instruments like a compass. This allows certain models to calculate how much time you will safely have based on a combination of factors including your rate of consumption, your remaining air supply, and your depth. No matter the interface, however, certain features are universally necessary. An easy to read display, a low battery warning indicator/alarm, and enriched air compatibility will ensure the safest dive by offering an easily readable display, security in the accuracy and ability of your computer's nitrogen level approximations, and the ability to use the now commonplace enriched air nitrox safely.
There are, of course, other customizable options for dive computers. These options are more preferential than critically important, but are very much worth knowing about for any diver's comfort and interests. For example, integrated interfaces can be made wireless in hoseless integration systems, wherein regulators transmit air supply information to your computer, which is most often worn on the wrist in this instance. Some dive computers more suitable for technical diving are also equipped to handle multiple types of gasses. Another optional safety feature, though not entirely necessary, is the audible warning, which sounds when diving at dangerous rates or toward dangerous thresholds. Computer download capabilities are also a useful tool for those interested in documenting detailed and accurate information on each dive in a convenient manner. However, before selecting a dive computer, no matter the diver's skill-level, experience, or technical interests in the computer, it is always important to consult a diving professional about the suitability, safety, and operational procedures for each dive computer.