English: A Kater's pendulum mounted in a stand, in the School of Civil Engineering, Channels and Ports (UPM). Kater's pendulum, invented by British captain Henry Kater in 1814, was a reversible freeswinging pendulum used as a gravimeter to measure the local gravitational acceleration during geophysical surveys in the 19th century. It is a bar with moveable weights and two knife edge pivots near either end. In use, the pendulum is suspended on a stand from one pivot resting on agate plates, as shown here, and swung, and its period timed, then turned upside down and suspended from the other pivot and its period timed. The weights are adjusted until the period is the same when swung from each pivot. Then the gravitational acceleration g can be calculated from the formula T = (g/L)^1/2, where T is the period and L is the measured distance between the two pivots.