Measurement of acceleration

An acceleration measuring device having a support and a proof mass, connected to each other by at least two flexures allowing displacement of the proof mass relative to the support, the support defining a space for displacement of the proof mass, the device being configured so that the modulus of the gradient of the force-displacement curve of the proof mass decreases with increasing displacement, for at least the part of the force-displacement curve corresponding to a range of movement of the proof mass within the device, wherein, the resonant frequency of oscillation of the proof mass is determined at least in part by the orientation of the device relative to the direction of the force due to gravity, such that the proof mass is capable of oscillating with a resonant frequency of 10 Hz or less, and wherein the proof mass has a mass of less than 0.1 grams, and wherein the modulus of the gradient of the force-displacement curve is the mathematic modulus of the gradient, |dF/dz|, of the force-displacement curve with force, F, plotted on the ordinate, and displacement, z, plotted on the abscissa,

• wherein the support, proof mass and flexures define a plane of the device, corresponding to a plane of oscillation of the proof mass,
• wherein each flexure has a rest shape extending in a continuous arc defining a length direction of the flexure from the support to the proof mass, and a width direction of the flexure is defined as a direction in the plane of oscillation of the proof mass and perpendicular to the length direction, and a depth direction of the flexure is defined as a direction perpendicular to the plane of oscillation of the proof mass and perpendicular to the length direction, and
• wherein the width of the flexure on average along the length of the flexure, is at most 10 μm and the depth of the flexure on average along the length of the flexure, is at least 150 μm.