Using the HMC5883L, the heading can be calculated without an acceleration sensor. However, the sensor must be guaranteed to be horizontal. If the compass is not horizontal, an acceleration sensor is needed to correct the error due to the tilt. The HMC5883L Set/Reset loop functions to perform an automatic degaussing before each data measurement to eliminate the offset present in the device itself, allowing the sensor to be tested in a "pure" magnetic field. It reduces the effects of "noise" interference and does not affect high frequency signal identification, set in Configuration Register A. The function of the sensor self-test can be activated by setting the register of the HMC5883L to determine whether the sensor is good or bad.