Simple sophistication characterizes this single-gas nitrox unit. It adjusts no-deco times based on time, depth, diver workload (based on breathing rates) and water temperature, yet its displays and programming modes are ultra clean.

Packaging By using two flat screens on a curved housing, the Air Z Nitrox offers large numerical displays on a relatively compact unit. Four touch-sensitive contacts are used to move through various modes and to change parameters. A long, slim wrist cinch accommodates a wide range of arm sizes without the bulk of heavy watchband-style straps.

Core functions The Air Z Nitrox accommodates one nitrox mix up to 50 percent, and there is no automatic default. Whatever mix you program into the computer stays there until it's changed. The maximum PO2 limit is adjustable from 1.2 ata to 1.95 ata. On the oxygen front, the Air Z Nitrox uses an "oxygen clock" to track oxygen toxicity. A CNS display in the center of the main screen shows the theoretical percentage of oxygen buildup in the diver's system. The maximum is 100 percent, but an alarm sounds at only 75 percent — although a diver has to work pretty hard to reach such a level. PO2 level is not displayed during the dive, but an alarm will sound when the max level is reached based on depth. Should a diver exceed the no-decompression time, the computer will display a deco-stop depth, stop time and total ascent time. Aggressive repetitive diving, cold water temperatures and high breathing rates will all trigger shorter no-deco times and/or longer deco stops. However, the real key to getting the most out of the Air Z Nitrox is to closely monitor ascent rate. Upon ascent, the CNS display is replaced with an ascent rate monitor. It tracks ascent rate as a function of percentage, with 100 percent meaning the diver is ascending at the maximum rate. At 110 percent an alarm sounds, increasing in volume as the percentage climbs. Violating the computer's ascent rate will significantly affect future dive times. The Air Z Nitrox's algorithm is designed to minimize the formation of microbubbles, which are more likely to form after "yo-yo diving," making ultra-fast ascents or blowing by a deco stop. In case of the latter, three minutes spent shallower than a required deco stop will send the Air Z Nitrox into SOS mode, in which it will not perform regular dive calculations for 24 hours. Even when this mode clears, dive times may be affected for up to three days.

Bonus While some air-integrated computers display remaining dive time based on whatever the limiting factor is on a given dive, either deco status or air consumption, the Air Z Nitrox always displays both no-deco time and remaining bottom time (RBT). No-deco time is shown on the main screen, and RBT, based on air consumption rate and a preset safety limit (say, 500 psi), is shown next to the air-pressure reading on the smaller screen. No toggling between screens is required.