Tables used to be the only option. At this point, nearly all scuba divers dive with a personal dive computer and it makes sense.
The computer monitors your depth, time, ascent rate, and no-deco limits in real-time. Dive tables are a fixed calculation. If you move between depths during a dive, it updates. Tables are set before you get in.
Wrist computers are the most common use now. These are small enough, readable underwater, and you'll use them as a regular watch too. Console models are available but not as many divers go that way these days.
Entry-level computers start around $300-odd and do everything the average diver would need. Features include depth, bottom time, NDL, dive logging, and sometimes a basic apnea mode. Mid-range adds air integration, nicer displays, and additional mix options.
What new divers overlook is how the computer handles. Some models are more cautious than others. view details A conservative setting gives you shorter bottom time. Liberal settings extend bottom time but at a thinner margin. Neither is wrong. It comes down to what you're comfortable with and your diving background.
Ask someone at a local dive store who uses multiple models before buying. Good dive stores will give you a straight answer on which ones hold up versus what's marketing. The better Cairns dive stores publish product guides and honest reviews online too