A processing apparatus, optionally integrated into a device having a plurality of sensors including a magnetometer, generates navigational state estimates for the device. The processing apparatus has a magnetometer-assisted mode of operation in which measurements from the magnetometer are used to estimate the navigational state and an alternate mode of operation in which the navigational state of the device is estimated without measurements from the magnetometer. For a respective time period, the processing apparatus operates in the alternate mode of operation. During the respective time period, the processing apparatus collects a plurality of magnetometer measurements and determines whether they meet measurement-consistency requirements. If the measurements meet the measurement-consistency requirements, the processing apparatus transitions to the magnetometer-assisted mode of operation. If the measurements do not meet the measurement-consistency requirements, the processing apparatus continues to operate in the alternate mode of operation.