What is formula for retardation?

Retardation, or deceleration, is the rate at which an object slows down. It is often calculated using the formula: ( a = \frac{\Delta v}{\Delta t} ), where ( a ) represents retardation, ( \Delta v ) is the change in velocity (final velocity minus initial velocity), and ( \Delta t ) is the time taken for this change. If the object is slowing down, ( \Delta v ) will be negative, resulting in a positive value for retardation.