A seismograph pen, also known as a STYLUS, is a device used to record seismic activity. It is typically attached to a seismograph and records the vibrations of the ground onto a paper chart. The STYLUS is usually made of metal and is connected to a spring-loaded arm that moves in response to the seismic waves. The STYLUS then traces the seismic waves onto the paper chart, creating a record of the seismic activity.