Dive computers have become the most common way of tracking your allowable bottom time for a given depth while diving. Yes, you can plan and execute a dive by planning a dive with a dive table, depth gauge and a dive watch, but with the rise of the scuba diving computer, these are now used less and less. A computer takes into account your current depth and dive time and applies this to a decompression model to track the dissolved nitrogen in your body. This allows you to change depth and have immediate updates of how long you can stay at a given depth at any point in your dive. Your dive is a combination of a depth gauge, bottom timer, and, sometimes a submersible pressure gauge (SPG) into a single display. Diving with one just makes sense.