- (IBAction)StartStop:(id)sender {
    if (startbutton == NO){
        [StartButton setTitle:@"Stop" forState:UIControlStateNormal];
        startbutton= YES;

        rundenzaehler = 0;
        RundenText = @"";
        [self Start];
        startDate = [[NSDate date] init];

    }else {
      [StartButton setTitle:@"Start" forState:UIControlStateNormal];
        startbutton= NO;
        [stopwatchTimer invalidate];
        stopwatchTimer = nil;
        startDate = nil;
    }
}

- (void)Start{
    [RundenTextView setText:@""];
    stopwatchTimer = [NSTimer scheduledTimerWithTimeInterval: 0.001 target:self selector:@selector(tick:) userInfo:nil repeats:YES];

    [stopwatchTimer fire];
}

- (void)tick:(NSTimer *)theTimer
{
    //NSTimeInterval interval = -[startDate timeIntervalSinceNow];

    NSTimeInterval interval =[startDate timeIntervalSinceNow] * -1000.0;

    int millis = ((int)interval)% 1000;
    int seconds = (((int)interval)/1000) %60;
    int minutes = (((int) (interval/1000) - seconds) / 60) % 60;
    int hours = (((int) interval/1000) - seconds - 60 * minutes) % 3600;


    ZeitString = [NSString stringWithFormat:@"%.2d:%.2d:%.2d:%.3d", hours,
                                 minutes, seconds, millis];

    [elapsedTime setText:ZeitString];
}