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