It's going to focus at that F2 point. And so the spark is discharged at the F1 point and then using your localization mechanism you put the stone at the F2 point. For your purposes, for gallstone lithotripsy you localize it with an ultrasound machine, which is #5 here. It's actually a very ingenious method of doing it. Ultrasound has attached to it a light sensing system. It has 6 red lights on it along an array on top of the ultrasound probe. It's like a little shield that goes over your hand when you're holding the ultrasound and in the ceiling are sensors that sense the angle and where exactly those 6 lights are and that can tell the machine then where the stone is. It's very ingenious.