Some methods for determining acceleration and tilt by use of pendulums and accelerometers

We consider the use of a system of horizontal and vertical pendulums to determine linear and rotational components of ground motion. Accelerometers can be viewed as a special case of pendulums. Fourth-order equations are always required for determining horizontal displacement unless the natural period of at least one sensor lies far below the passband of interest. Applications to guidance and to seismology are mentioned briefly.