A vibrating structure gyroscope, comprising: a resonant structure arranged to vibrate under stimulation from a primary drive electrode; a drive system arranged to vibrate the vibrating structure at a resonance frequency, the drive system comprising the primary drive electrode arranged to induce motion in the vibrating structure, and a primary sense electrode arranged to sense motion in the vibrating structure; an automatic gain control unit arranged to vary an amplitude of a drive signal applied to the primary drive electrode; and a controller arranged to operate the gyroscope such that: in a first mode of operation, the automatic gain control unit varies an amplitude of the drive signal; and in a second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level; characterised in that: in the first mode of operation, the automatic gain control unit varies the amplitude of the drive signal within an operating range defined by a lower bound and an upper bound; and in the second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level outside of the operating range; and when the gyroscope is operated in the second mode of operation, the controller: measures an amplitude of a sense signal from the primary sense electrode after a predetermined time period; determines an oscillation cycle count during said predetermined time period; and determines a quality-factor of the gyroscope from said measured amplitude and oscillation cycle count. a resonant structure arranged to vibrate under stimulation from a primary drive electrode; a drive system arranged to vibrate the vibrating structure at a resonance frequency, the drive system comprising the primary drive electrode arranged to induce motion in the vibrating structure, and a primary sense electrode arranged to sense motion in the vibrating structure; an automatic gain control unit arranged to vary an amplitude of a drive signal applied to the primary drive electrode; and a controller arranged to operate the gyroscope such that: in a first mode of operation, the automatic gain control unit varies an amplitude of the drive signal; and in a second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level; characterised in that: in the first mode of operation, the automatic gain control unit varies the amplitude of the drive signal within an operating range defined by a lower bound and an upper bound; and in the second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level outside of the operating range; and in a first mode of operation, the automatic gain control unit varies an amplitude of the drive signal; and in a second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level; characterised in that: in the first mode of operation, the automatic gain control unit varies the amplitude of the drive signal within an operating range defined by a lower bound and an upper bound; and in the second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level outside of the operating range; and in the first mode of operation, the automatic gain control unit varies the amplitude of the drive signal within an operating range defined by a lower bound and an upper bound; and in the second mode of operation, the automatic gain control unit sets the amplitude of the drive signal to a predetermined level outside of the operating range; and when the gyroscope is operated in the second mode of operation, the controller: measures an amplitude of a sense signal from the primary sense electrode after a predetermined time period; determines an oscillation cycle count during said predetermined time period; and determines a quality-factor of the gyroscope from said measured amplitude and oscillation cycle count. measures an amplitude of a sense signal from the primary sense electrode after a predetermined time period; determines an oscillation cycle count during said predetermined time period; and determines a quality-factor of the gyroscope from said measured amplitude and oscillation cycle count.