Introduction: the story of inertial sensors
The story started nearly two centuries ago with French physicist Leon Foucault. He used his famous pendulum – a 28kg brass-coated lead bob with a 67 meter long wire from the dome of the Panthéon, Paris – to demonstrate the rotational rate of the earth in 1851, and then went on to perfect the measurement using a gyro in 1852.
In order to grasp the underlying mechanics, one has to imagine that the plane of oscillation of the pendulum remains fixed relative to the far distant masses of the universe, while Earth rotates underneath it.
Figure 1: Foucault Pendulum, Pantheon, Paris.
Gyroscopes and accelerometers -- also called inertial sensors -- remained scientific curiosities for almost a century but had a huge impact during the Second World War, as they were used in a large set of applications such as ship navigation, guided missiles, battery fire control, aircraft artificial horizon and flight controls.