With all the attention to non-simple pendulums of late, perhaps some readers will be
interested
in the following old one of my webpages:
http://physics.mercer.edu/petepag/pend.htm#torsion
  The 'pendulum' titled 'tiltmeter' is an example of a system for which the influence of
earth tilt can be greatly 'magnified'.as the operator changes the orientation of the torsion
wire, causing approach toward a critical value.
A system similar to it was used by one of my students in the early 1990's to study
chemisorbed
gases on metals.  With it he was the frist person to observe (accidently) earth hum having
frequencies below a few milliHertz.  There was much, much geoscience interest in later,
similar earth oscillations at mainly higher frequency, starting about 1998.
    Randall