Years ago, dive tables were the only option. Now, most recreational divers dive with a wrist-mount computer and for good reason.
A dive computer monitors your depth, time, ascent rate, and no-deco limits in the moment. Dive tables are a fixed calculation. If you change depth mid-dive, it updates. A table can't.
Wrist-mount computers are the most common use these days. These are small enough, readable underwater, and you'll use them as a watch as well. Console computers are an option discover this but not as many divers choose them these days.
Basic computers start around $300-odd and handle everything the average diver needs. You get depth, dive time, NDL, log function, and often a basic apnea mode. The $500-800 range includes wireless air monitoring, improved screens, and more nitrox modes.
The one thing people overlook is algorithm differences. Certain computers are more conservative than others. A tighter algorithm means shorter NDL. Looser settings allow longer bottom time but with less buffer. Both work. It comes down to your style and how experienced you are.
Worth talking to people at a dive shop who's used multiple brands first. Staff will have a straight answer on which ones hold up and what isn't just marketing. The better Cairns dive stores have buying guides and comparisons online as well