A MEMS structure for a combined gyroscope and accelerometer unit (100) based on in-plane vibratory movements comprises a proof mass (101) and comb-drives (102) operable to cause the proof mass (101) to resonate in the x-direction, commonly referred to as the primary mode. Under the influence of a rotation Ωz around the z-axis, a Coriolis force acting in the y-direction results. This excites the secondary (or sense) mode. A set of parallel-plate capacitors 103 are provided to enable position readout along the secondary axis. In addition to the above, the comb-drive capacitors (102) of the primary mode can also be used for readout of position along the primary axis, and the parallel-plate capacitors (103) for actuation along the secondary axis. This can be achieved either by time-multiplexing these capacitors (102, 103) or by providing separate sets of capacitors (102, 103) for sensing and actuation along each axis. The unit can operate in separate ΣΔ force-feedback loops with respect to both axes. This force-feedback approach is already known for readout of the secondary mode of MEMS gyroscopes. It has not previously been applied to the primary mode of a gyroscope for the measurement of a component of acceleration.