iphone NStimer slows down when swipe on the screen
===

in my application,I have implemented NSTimer to count time.I have swipe detection and when 
the user swipes on the screen,animation runs continuously.my question is when I swipe
on the screen(left/right continuously) NSTimer slows down.
can anybody tell me how to solve this problem?

//code

    gameTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/100
                                                          target:self
                                                        selector:@selector(updateGameTimer)
                                                        userInfo:nil
                                                        repeats:YES];
    
    -(void)updateGameTimer
    {
        counter++;
        tick++;
        if(tick==100){
            tick = 0;
            seconds += 1;
        }
        if(counter==100){
            counter = 0;
        }
        timerLabel.text = [NSString stringWithFormat:@"%i.%02d",seconds,counter];
    } 

