Как два UIScrollView сделать зависимыми между собой?

class ChartViewController: UIViewController {

    @IBOutlet weak var chartAreaScrollView: UIScrollView! // First UIScrollView
    @IBOutlet weak var timeScrollView: UIScrollView! // Second UI ScrollView

    override func viewDidLoad() {
        super.viewDidLoad()

        chartAreaScrollView.delegate = self as! UIScrollViewDelegate 
        timeScrollView.delegate = self as! UIScrollViewDelegate    
    }
    
    
    extension ChartViewController: UIScrollViewDelegate {// Сообщение (Declaration is only valid at file scope)
        func scrollViewDidScroll(scrollView: UIScrollView) {

            self.chartAreaScrollView.contentOffset = scrollView.contentOffset
            self.timeScrollView.contentOffset = scrollView.contentOffset
        }
    }

}

extension ChartViewController: UIScrollViewDelegate { // Сообщение (Declaration is only valid at file scope)
        func scrollViewDidScroll(scrollView: UIScrollView) {

            self.chartAreaScrollView.contentOffset = scrollView.contentOffset
            self.timeScrollView.contentOffset = scrollView.contentOffset
        }
    }