Stopping distance testing involves performing an emergency stop in a test vehicle and measuring the distance required to come to a stop. This can be measured either from the length of the skid marks left by the vehicle, or by the "chalk-to-gun" method, where the brakes are connected to a small gun filled with chalk powder, which marks the point when the brakes were applied. This has the advantage of measuring the full stopping distance, while simply measuring the skid marks only measures the distance from the point where the wheels began to lock or slip.[1]