Eye-position recordings have been used to produce detailed information about sampling and search behavior. The melding of magnetic head-tracking technology with eye-tracking systems has allowed for freer head movement, but not without problems. Although the requisite calibrations made before and after a reading might indicate good eye-tracking accuracy, point-of-gaze errors can occur if the reader leans toward a display, such as a film alternator. The error results from the characteristic that large metal masses can distort magnetic fields, leading to false magnetic sensor data. Corrections for this type of error have involved mapping the exact location and orientation of the magnetic sensor in the magnetic field by using a precision positioning device. We have devised a much cheaper method that relies on a fixture that holds the magnetic sensor in identical positions, with and without the distorting effect.