Patent ID: 7210236

Claim:
A method of measuring a magnetic offset of a geomagnetic sensor equipped in a portable information terminal apparatus, the geomagnetic sensor having a magnetic sensitivity to a geomagnetic field in a plurality of axes of a coordinate system, and being affected by magnetization to cause the magnetic offset, the method comprising: a data measurement step of measuring an output of the geomagnetic sensor and acquiring a plurality of measurement data of the geomagnetic field, each measurement data being represented by a data point in the coordinate system; an offset estimation step of estimating an offset value of the magnetic offset of the geomagnetic sensor from the plurality of the measurement data of the geomagnetic field, the offset value being represented by an offset point in the coordinate system; a mean value calculation step of calculating distances between the offset point corresponding to the offset value and a plurality of the data points corresponding to the plurality of the measurement data used for estimating of the offset value, and further calculating a mean value of the calculated distances between the offset point and the plurality of the data points; a standard deviation calculation step of calculating a standard deviation of the calculated distances with respect to the calculated mean value of the distances; and a validity judgment step of judging validity of the estimated offset value on the basis of the calculated standard deviation.