Diving watchIt is a waterproof timepiece with a method for measuring elapsed time underwater. For recreational open-air diving, the dive watch should be at least 140 feet deep.
Depth gaugeAn analog or digital gauge that records the current and (usually) maximum depth reached during a dive.
Diving pressure gauge or SPGDisplays the amount of air remaining in the diving cylinder. They can be mounted on hoses of different lengths-or in the case of gauges used with spare tanks-they can be mounted on the first stage of the regulator.
Underwater compassIt can be analog or electronic. For accurate underwater navigation, many divers prefer a compass mounted on a combination tablet and compass board, which follows the heading while holding with both hands.
Depth / time capsuleDisplays the current and maximum depth reached during the dive, as well as the elapsed time, and they often store this information for multiple dives. These instruments look similar to dive computers, but they do not calculate a safety factor. Depth capsules are often used as backup timers, or as the main timer for divers, using dive watches to calculate their own bottom time and surface interval.
Dive computerAutomatically track time and depth changes, calculate safety time remaining during a dive, and plan time intervals and allow time and depth information for subsequent dives. Some dive computers are air-integrated and include information on tank pressure and estimated remaining air time.