Years ago, dive tables were the standard. Today, nearly all scuba divers wear a personal dive computer and they should.
A dive computer tracks your depth, time, speed of ascent, and no-decompression limits in the moment. Dive tables are a fixed calculation. When you move between depths mid-dive, the computer recalculates. A table can't.
Wrist-mount computers are what most people use at this point. They're small enough, easy to read, and you'll use them as a daily watch between dives. Hose-mounted models are still around but less divers choose them these days.
Entry-level computers run about $250-400 and do everything most divers would need. You get depth tracking, time, no-deco limits, a logbook, and sometimes a basic freediving mode. Mid-range includes transmitter compatibility, improved readability, and additional nitrox options.
Something buyers don't think about is conservatism settings. Some computers are more cautious than others. A conservative computer means shorter bottom time. Liberal ones allow longer time but at a thinner buffer. Neither is wrong. It just personal preference and how experienced you are.
Ask someone at a local dive store who uses various models before buying. They'll give you real-world feedback on which ones hold up versus what's website marketing. The better Cairns dive stores put out gear reviews and rundowns on their sites too