An orientation-determining system determines a person's compass orientation from data generated by one or more sensors embedded within a portable device transported by the person. In some scenarios, the system uses the person's initial orientation to calculate an initial orientation delta describing a difference between the person's initial orientation and an initial orientation of the device. In other scenarios, the system calculates the person's current orientation based on an initial orientation of the device and a known or assumed orientation delta. The system can apply the orientation delta to the device's current orientation to determine the person's current orientation. The system can update the orientation delta based on any changes to the orientation of the person or the device.