Mares Smart dive computer has four measurements to help you monitor your dive and stay safe. It is multi-gas set up for decompression diving. It has timers for: air, nitrox, bottom timer and freedive. You can light up to see better in deeper, darker waters. The crystal clear scratch-resistant mineral glass display will stay intact through rock bumps, boat bums and reef scratches. Battery is replaceable. Features:Crystal clear scratch-resistant mineral glass display4 dive modes: air-nitrox-bottom timer and freediveMulti-gas for decompression divingBacklight on demandReplaceable battery