© Copyright (2017) by International Astronautical Federation All rights reserved.A three-axis magnetometer (TAM) is as an essential attitude sensor for low-Earth orbiting small satellites. Being light, small and inexpensive make TAM an ideal attitude sensor specifically for nanosatellite missions. Nonetheless, it is a known fact that the accuracy of the TAMs suffers from the electromagnetic interference (EMI) on-board the nanosatellites. Recent studies show that on small satellites the magnetometer errors vary over time as the EMI changes. Variation in the magnetometer errors may be a result of the change in the state of the magnetic torquers, as well as interference from the nearby electronics and ferromagnetic materials (soft irons). Despite a number of researches about time-varying magnetometer errors, the calibration algorithms are usually applied ad hoc after the launch since the researchers lack information about the error characteristics. This study presents the preliminary results for an ongoing investigation that aims real-time calibration of time-varying magnetometer errors. In this research, our first aim is to model the time-variation of the magnetometer error terms with experiments. In this paper we discuss our method to model the time-variation in the magnetometer errors. The theory is supported with the experiments that we conducted using an integrated TAM, gyro and accelerometer sensor which is suitable for nanosatellite applications. The experiment setup is introduced and the practical issues concerning a realistic magnetometer error model derivation are discussed.