Seismograph is used to measure ---

A seismometer is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with "seismograph".

Seismographs are instruments used to record the motion of the ground during an earthquake.

They are installed in the ground throughout the world and operated as part of a seismographic network. The earliest "seismoscope" was invented by the Chinese philosopher Chang Heng in A.D. 132.

This did not, however, record earthquakes; it only indicated that an earthquake was occurring. The first seismograph was developed in 1890.