Disclosed is a respiratory apparatus (100) for providing therapy for a patient with disordered breathing. The respiratory apparatus (100) comprises a flow generator (120), one or more sensors and a processor (116). The flow generator (120) has a blower (130) to generate a flow of breathable gas for a patient interface at a pressure above atmospheric pressure. The blower (130) comprises a motor. The one or more sensors (104, 106, 108, 110) are configured to respectively output measurement of one or more of: a) a pressure of the flow of breathable gas； b) a temperature of the flow of breathable gas； c) a speed of the motor； and d) a flow rate of the flow of breathable gas. The processor (116) comprises an altitude estimation unit. The processor (116) is configured to determine an estimate of an altitude of the respiratory apparatus (100) based on the output measurement from the one or more sensors. And the processor (116) is also configured to control the blower (130) based on the estimate of the altitude.
