         startTrackingValue = self.on
         didChangeWhileTracking = false
         
-        let activeKnobWidth = self.bounds.size.height - 2 + 5
+        let activeKnobWidth = knobSize.width + 5
         isAnimating = true
         
         UIView.animateWithDuration(0.3, delay: 0.0, options: UIViewAnimationOptions.CurveEaseOut | UIViewAnimationOptions.BeginFromCurrentState, animations: {

    *   optionally make it animated
    */
    private func showOn(animated: Bool) {
        let normalKnobWidth = self.bounds.size.height - 2
        let activeKnobWidth = normalKnobWidth + 5
        if animated {
            isAnimating = true

    *   optionally make it animated
    */
    private func showOff(animated: Bool) {
        let normalKnobWidth = knobSize.width
        let activeKnobWidth = normalKnobWidth + 5
        
        if animated {
