/**
  * Calculate vertical ratio for activity
  * Use this method if trackdata is not available
  * @param \Runalyze\Model\Activity\Entity $activity
  * @return int [%o]
  */
 public static function forActivity(Activity\Entity $activity)
 {
     if ($activity->verticalOscillation() > 0 && $activity->strideLength() > 0) {
         return round(100 * $activity->verticalOscillation() / $activity->strideLength());
     }
     return 0;
 }