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 as sensitive ground rotation sensors for 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. We deploy these at the observatories to guard against the effects of wind bending the concrete foundation of the facility.
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 were 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: