An oscillation device comprising: a system capable of undergoing transitions between different energy states, the transitions defining at least a first resonance frequency and a second resonance frequency; an excitation device arranged to induce the system to undergo such transitions; a detection device arranged to detect a response of the system caused by the excitation device, to produce an output; and a controller arranged to receive the output, to control the excitation device to stimulate said transitions, and to obtain signals corresponding to at least the first and second resonance frequencies, characterized in that: the controller is also arranged to process the obtained signals corresponding to at least the first and second resonance frequencies to produce a corrected output signal that is compensated against at least one environmental influence on the resonance frequencies of the system; wherein the corrected output signal of the controller is a corrected first resonance frequency, wherein the corrected output signal is obtained using the ratio or difference of the obtained signals corresponding to first and second resonance frequencies, in conjunction with a predetermined coefficient of change of the first resonance frequency with an environmental influence; wherein the system comprises at least one endohedral fullerene; and wherein the environmental influence is at least one of temperature and magnetic field. a system capable of undergoing transitions between different energy states, the transitions defining at least a first resonance frequency and a second resonance frequency; an excitation device arranged to induce the system to undergo such transitions; a detection device arranged to detect a response of the system caused by the excitation device, to produce an output; and a controller arranged to receive the output, to control the excitation device to stimulate said transitions, and to obtain signals corresponding to at least the first and second resonance frequencies, characterized in that: the controller is also arranged to process the obtained signals corresponding to at least the first and second resonance frequencies to produce a corrected output signal that is compensated against at least one environmental influence on the resonance frequencies of the system; wherein the corrected output signal of the controller is a corrected first resonance frequency, wherein the corrected output signal is obtained using the ratio or difference of the obtained signals corresponding to first and second resonance frequencies, in conjunction with a predetermined coefficient of change of the first resonance frequency with an environmental influence; wherein the system comprises at least one endohedral fullerene; and wherein the environmental influence is at least one of temperature and magnetic field. the controller is also arranged to process the obtained signals corresponding to at least the first and second resonance frequencies to produce a corrected output signal that is compensated against at least one environmental influence on the resonance frequencies of the system; wherein the corrected output signal of the controller is a corrected first resonance frequency, wherein the corrected output signal is obtained using the ratio or difference of the obtained signals corresponding to first and second resonance frequencies, in conjunction with a predetermined coefficient of change of the first resonance frequency with an environmental influence; wherein the system comprises at least one endohedral fullerene; and wherein the environmental influence is at least one of temperature and magnetic field.