In this work an attempt is made to develop a decelerometer, an experimental facility or apparatus, for measuring the braking efficiency of vehicle. The first attempt is made to design, develop & analyse the mechanical decelerometer. The trials test results are taken on Maruti - 800 car and Maruti - Omni Van. From graphs, it is seen that the theoretical braking efficiency and the efficiency shown by Decelerometer are in good agreement. The percentage difference got is more than 14%. This shows instrument does not meets the exact requirement, armature reliability, parallax error in design of...