Which method of control is used to specify an exact duration for the impact of rounds?

The method of control that is specifically used to specify an exact duration for the impact of rounds is Duration. This control method is designed to define how long the fire will continue to impact a designated target area. It enables the fire support team to plan and execute fire missions that maintain consistent and controlled fire over a set period, which is crucial in operations where sustained fire effects are needed to neutralize or suppress enemy positions.

Using Duration allows different units to synchronize their operations effectively, ensuring that the support provided matches the operational needs on the ground without exceeding or falling short of the intended fire support duration. This level of control is particularly valuable in complex scenarios that require precise timing and management of firepower, facilitating operational effectiveness and safety.