Computers
Purpose
Dive computers have become an essential part of your scuba diving gear. A dive computer will provide valuable information before, during, and after each dive. Before your dive, the computer will help you with depth and bottom time planning. During the dive, you can see important data such as current depth, maximum depth, dive time, no-deco lmit, deco time, ascent rate, water temperature. After the dive, you will have access to the dive log to show you all the detail of your dive.
Features
Style
Dive computers can be either part of your console along with a pressure gauge (and compass) or it can be worn on your wrist. Wrist style computers can also be worn while snorkeling and free diving. In terms of size, a wrist style can be a smaller, watch-size or a larger, hockey-puck size.
Air Integration
Some dive computers will allow you to integrate the air pressure reading from your scuba tank. In a console style, the computer will replace your depth and pressure gauges. In a wrist style, you will need a transmitter that fits into the first stage of your regulator, usually you will still have a backup set of analog gauges in a console as well.
Nitrox Compatible
Most dive computers nowadays will accommodate different gas mixes including Nitrox. Even if you don't dive Nitrox now, this is something to consider as an option in the future.
Downloadable
After your dives, you may want to download the data to your PC, tablet, or even smartphone to add to your logbook. Information usually includes maximum depth, average depth, dive time, water temperature, alarm warnings, and a graphical depiction of your dive. Downloading cables are not included with all computers but may be purchased separately. Some dive computers may also use Bluetooth and other wireless technologies.
Alarms
These may be visual or audible and will usually indicate warnings such as ascent rate, exceeding NDL, exceeding max depth, etc. Some dive computers may also vibrate to indicate an alarm.
Modes
All computers will have a Dive mode which give you information during the dive including depth, bottom time, and your no-decompression limit. The Log mode is used on the surface and will give you the information from past dives, including max depth, average depth, actual bottom time, water temperature just to name a few. The Plan mode will be useful prior to the dive as it will indicate a variety of depths and the no-decompression limit at that depth, based on your immediate dive history, to help plan your next dive. Other modes that may be available depending on the computer model include Gauge mode, which allows you to run the computer as a bottom timer and depth indicator only, and Freedive mode, which allows you to record your freediving/snorkeling activities.
Other Funcutions and Features
These will vary from computer to computer and are worth a detailed look. Every diver has different needs and preferences you should look for what appeals to you and your diving style. User changable battery, digital compass and multiple gas mix are a few examples.
Analog Gauges
Even though a dive computer gives you a lot of vital information, it's always nice to have a backup in case your computer fails, batteries die, or you forget to wear your computer. Good ol' fashioned gauges will provide you with your depth and air pressure to ensure you can still go diving, although you will have to use your dive tables for planning and logging your dive.