It is a compound pendulum with adjustable knife edges placed respectively at the center of suspension and near the center of oscillation.
According to Kater's principle, when we suspend the pendulum upside down from the point of oscillation, the frequency of the oscillation remains the same.
Uses
Kater's pendulum is used as a gravimeter, a device used to measure the acceleration due to gravity.
They are used in pendulum clocks, in scientific instruments such as accelerometers and seismometers.