Abstract: An oxygen setpoint controller (SPC) and a user's display for a rebreathing apparatus wherein the user exhales oxygen depleted breath into a closed rebreathing loop, the CO2 is scrubbed from the exhaled gases, oxygen is added to the rebreathing loop to maintain the oxygen at a specified partial pressure, and the oxygen enhanced gases in the rebreathing are provided to the user. The SPC is able to detect the failure of any of the oxygen sensors and provide an alarm condition to the user. The SPC further operates to provide dive data such as rate of ascent, time of dive, depth, and PPO2 to the uses, and to store and retain dive data for further review. The SPC further provides numerical dive data to a heads up display (HUD). The HUD further includes a tricolor LED displaying selected analog parameters.