Properly Holding the Indicator and the Mask
Place the indicator in the palm of the left hand as shown in the photo.
Hold the indicator with the ring finger and the pinkie finger.
Still remembering to use the left hand, place the index finger and middle finger on the lower side portion of the mask.
Here's another view on where exactly the fingers go.
Clamp down around mask pads front and back. Don't forget that you are still holding your indicator.
A full view. Notice the placement of the fingers to the area of the mask. Also, notice the placement of the indicator at the bottom of the hand.
Steve Mattingly, Arizona Umpiring Academy instructor, uses the exact method that is taught at the clinics held by the AZUA.

Arizona Umpiring Academy instructor, Ted Barrett, uses proper handling of the mask.