This invention relates generally to multi-reflection electrostatic systems, and more particularly to improvements in and relating to the Orbitrap electrostatic ion trap. A method of operating an electrostatic ion trapping device having an array of electrodes operable to mimic a single electrode is proposed, the method comprising determining three or more different voltages that, when applied to respective electrodes of the plurality of electrodes, generate an electrostatic trapping field that approximates the field that would be generated by applying a voltage to the single electrode, and applying the three or more so determined voltages to the respective electrodes. Further improvements lie in measuring a plurality of features from peaks with different intensities from one or more collected mass spectra to derive characteristics, and using the measured characteristics to improve the voltages to be applied to the plurality of electrodes.