Seismic waves are studied by seismologists and measured by a seismograph or seismometer. They focus on seismic and tectonic activity by using a seismograph. This facility hosts interpretive displays on earthquakes, plate tectonics, and a working seismograph. An early seismograph of Zhang Heng's design used to be housed at the observatory. The modern broadband seismograph can record a very broad range of frequencies. Currently Mount Garibaldi does not have a seismograph closer than . A seismogram is a graph output by a seismograph. Gleason Public Library also contains a seismograph. Modern digital seismograph records are better adapted to direct computer use. Technological innovations, such as the wheelbarrow, paper and a seismograph, were invented during this period. The first efforts at this method used manual data reduction from paper seismograph charts. The output of a digital seismograph can be simply input to a computer. Each rotation of the seismograph drum is thirty minutes. The school is one of the few in the United States to have a seismograph. A complete instrument package that records seismic signals is called a seismograph.