function thumbNext() {
  if((thumbsPosition - (3*thumbSize)) > (thumbsWidth)*(-1)) {
    var thumbsLeft = parseFloat(thumbsElement.style.left, 10);
    thumbsElement.style.left = thumbsPosition - step + 'px';
    thumbsPosition = thumbsPosition - step;
    if(stop !=1) {
      setTimeout(thumbNext, interval);
    }
  }
}

function thumbPrev() {
  if(thumbsPosition < 0) {
    var thumbsLeft = parseFloat(thumbsElement.style.left, 10);
    thumbsElement.style.left = thumbsLeft + step + 'px';
    thumbsPosition = thumbsPosition + step;
    if(stop !=1) {
      setTimeout(thumbPrev, interval);
    }    
  }  
}