Along with Krishna Venkateswara and the Eöt-Wash Group, I develop and build precision beam balances with resonant periods of 120 to 300 seconds that are used to sense minute ground rotations for the seismic isolation systems of the LIGO gravitational wave observatories. These sensors can sense rotations of ~0.1 nrad which is roughly the angle you would get if you placed a grain of rice on one end of the Great Wall of China and drew a triangle between the other end of the Great Wall and the top of the grain of rice. These sensors help mitigate the effects of the slight bending of the concrete foundation that happens when the wind pushes on the walls of the observatory.
As side benefit, these devices have allowed us to study seismic waves in a unique way. By combining the tilt signal with a nearby seismometer, we are able to extract geological properties using just two devices as compared to the traditional way which requires deploying an array of seismometers.
Rotational seismic wave from Magnitude 7.9 earthquake in Papua New Guinea measured at the LIGO Hanford Observatory: