Adjusting the arc and radius of a rotor is an easy task. Most residential rotors are adjusted the same way. There are two adjustments that can be made on rotors, arc and radius. Arc: The degrees of coverage of a sprinkler from one side of pattern to the other. A 90-degree arc would be a quarter-circle sprinkler. In other words, the arc is how far to the left and to the right the sprinkler will be adjusted to rotate. Radius: The distance of throw from the sprinkler head to the furthest point of water application.