BNO055 has BSX sensor fusion library running inside Atmel SAMD20J18 MCU. BNO055 has built-in two 9-axis sensor fusion modes called NDOF and NDOF_FMC_OFF. If you chose NDOF mode, then gyro data will be used to quickly calibrate the mag. This means that you don't even need to finish a full round of Figure-8 motion to calibrate the mag. Maybe before the half way of Figure-8 motion the mag is already fully calibrated and ready to go. If you chose NDOF_FMC_OFF mode, then only mag data will be used to calibrate the mag.
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