Aqua Lung i550 Dive Computer 3 operating modes. Air, Nitrox, Gauge (with run timer) User changeable battery and data retention. Maintains settings and calculations between battery changes Gas integrated. Tank Pressure is easy to read in the large face screen. Our patented Gas Time Remaining Algorithm provides calculations in real time, allowing accurate gas management Backlighting. For easy reading in low light. User-updatable software gives access to the latest features and upgrade (Must purchase optional download cable. Cable is included on i550 Pro Pack) Audible alarms and additional high-visibility LED warning light for additional safety