Adjusting the arc and radius of an MP Rotator is an easy task. There are two adjustments, arc and radius, that can be made on an MP Rotator. 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, 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.