During a countdown to a coupling, how many car lengths must the engineer stop within?

During a countdown to a coupling, the engineer must stop within 1 car length to ensure a safe and effective coupling process. This requirement is crucial because it allows for precise control over the train's speed and positioning, minimizing the risk of accidents or damage to the railcars during the coupling maneuver. Stopping within 1 car length enables the crew to make necessary adjustments and ensures that the couplers align properly, facilitating a smooth joining of the cars. This practice emphasizes safety and operational efficiency in rail operations.