Dive computers are dynamic dive tables.
They help eliminate the hassle of trying to remember how to use dive tables to calculate your pressure group. Upon ascending, the dive comp will assist you in calculating a depth for your safety stop and for how long. This in effect, gives divers more bottom time. The main difference between using dive comps and dive tables is that dive tables calculate a diver's pressure group by using his maximum depth against the total bottom time. Most of the time, this does not truly reflect a diver's dive profile.