Cross-Axis projection error in optically pumped magnetometers and its implication for magnetoencephalography systems

•The presented manuscript describes an error source commonly encountered in optically pumped magnetometers (OPMs) in presence of remnant static fields that we call “Cross-Axis projection Error”.•Through theoretical analysis, the cross-axis projection error is studied and simulated, and through experiment, it is induced in the measured OPM response. The simulation and experiment results are in good agreement.•The impact of cross-axis projection error on the localization capability of OPM-based magnetoencephalography systems (OPM-MEG) is simulated and analyzed.•We find that cross-axis projection error can be alleviated by keeping the remnant field below ±1 nT.