问如何用秒表显示准确的时间？

EN

import UIKit

class ViewController: UIViewController {

    var counter = 0
    var timer = Timer()

    @IBOutlet weak var timerLbl: UILabel!

    @IBAction func startBtn( sender: Any) {
        timer.invalidate()
        timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(ViewController.updateTimer), userInfo: nil, repeats: true)

    }

    @IBAction func stopBtn( sender: Any) {
        timer.invalidate()
        counter = 0
    }

    func updateTimer() {
        counter += 1
        timerLbl.text = "(counter)"
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}