an inertial device for measuring deceleration (the reduction of the speed of a transport vehicle per unit time). A liquid, a pendulum, or a weight suspended on springs is used in a decelerometer.

The primary component of a pendulum decelerometer is a pendulum suspended on an axis in a transparent housing. The device is secured to the windshield or dashboard of a motor vehicle by means of rubber suction cups and is installed in such a way that the pendulum assumes a position opposite the zero mark on the scale. During controlled braking of the vehicle, the pendulum is deflected by the inertial force (equal to the braking force), and the deflection is recorded by the arrow pointer. Deceleration is determined on the basis of the deflection of the pendulum. Decelerometers may be of the display or recording types.