Ah. The dreaded HS-1015 Stringer Invisible Rivets. I have been riveting in a horizontal position placing the frame on two banker boxes with a soft blanket to position. For the invisible rivets I balanced the tungsten rivet bar on my first two fingers and pushed up on the rivet. After placing the rivet gun on the skin, I reposition the rivet bar to "feel" a horizontal position. A known burst of the gun set the rivet to pretty darn close to what I wanted. I used a telescoping mirror to inspect results, all worked well! (Black Gorilla tape is used on bucking bar to protect stringer from damage.) PM me for a video of this technique if desired - dl