An inertial sensor comprising: a frame, a resonator assembly fixed to the frame comprising a first and second resonator (1,2) coupled to one another by a mechanical coupling, a drive means coupled to the resonator assembly for driving the first and second resonators (1,2) to vibrate, wherein the resonator assembly is configured such that energy is transferred between the first and second resonators (1,2) through the mechanical coupling, an amount of energy transferred through the mechanical coupling being dependent on the value of an input measurand acting on one of the first and second resonators, and wherein the resonator assembly has a first resonant frequency at which an amplitude of vibration of the first resonator is maximised and a second resonant frequency at which an amplitude of vibration of the second resonator is maximised, when the input measurand has a first value; characterised by comprising an electrical circuitry, a pumping means coupled to the resonator assembly for applying a pumping signal to the resonator assembly, the pumping means controlled by the electrical circuitry, and a sensor assembly configured to detect the amplitude of oscillation of the first resonator at the first resonant frequency and the amplitude of oscillation of the second resonator at the second resonant frequency; wherein the electrical circuitry is configured to control the pumping means to apply a pumping signal that has a frequency substantially equal to a difference between the first resonant frequency and the second resonant frequency; wherein, when the input measurand has the first value, the signal from the pumping means adjusts an amplitude ratio of the amplitudes of oscillation of the first and second resonator (1,2) detected by the sensor assembly so that the amplitude ratio is within a predetermined amplitude ratio range over an expected range of input measurand values; and wherein an output of the inertial sensor is based on the amplitude ratio. a frame, a resonator assembly fixed to the frame comprising a first and second resonator (1,2) coupled to one another by a mechanical coupling, a drive means coupled to the resonator assembly for driving the first and second resonators (1,2) to vibrate, wherein the resonator assembly is configured such that energy is transferred between the first and second resonators (1,2) through the mechanical coupling, an amount of energy transferred through the mechanical coupling being dependent on the value of an input measurand acting on one of the first and second resonators, and wherein the resonator assembly has a first resonant frequency at which an amplitude of vibration of the first resonator is maximised and a second resonant frequency at which an amplitude of vibration of the second resonator is maximised, when the input measurand has a first value; characterised by comprising an electrical circuitry, a pumping means coupled to the resonator assembly for applying a pumping signal to the resonator assembly, the pumping means controlled by the electrical circuitry, and a sensor assembly configured to detect the amplitude of oscillation of the first resonator at the first resonant frequency and the amplitude of oscillation of the second resonator at the second resonant frequency; wherein the electrical circuitry is configured to control the pumping means to apply a pumping signal that has a frequency substantially equal to a difference between the first resonant frequency and the second resonant frequency; wherein, when the input measurand has the first value, the signal from the pumping means adjusts an amplitude ratio of the amplitudes of oscillation of the first and second resonator (1,2) detected by the sensor assembly so that the amplitude ratio is within a predetermined amplitude ratio range over an expected range of input measurand values; and wherein an output of the inertial sensor is based on the amplitude ratio.