An implantable or other ambulatory medical apparatus comprises a posture sensing circuit, a physiologic sensing circuit that senses a time varying physiologic signal, and a processor circuit. The processor circuit includes a posture calculation circuit and a measurement circuit. The posture calculation circuit determines a posture of the subject using posture data obtained using the posture signal and determines when the posture of the subject is steady state. The measurement circuit derives a physiologic measurement using physiologic data extracted from the physiologic signal during at least one time period when posture is determined to be steady state and provides the physiologic measurement to at least one of a user and a process in association with the determined steady state posture.