I want to know the answer to the following question:
A seismometer during the Han dynasty used what type of pendulum?
All the background I'm provided with is that "Science and technology during the Han period saw significant advances, including papermaking, the nautical steering rudder, the use of negative numbers in mathematics, the raised-relief map, the hydraulic-powered armillary sphere for astronomy, and a seismometer employing an inverted pendulum.". Is that enough to answer the question?