Bill, FWIW - I had a little trouble with mine on the first outing, due, in part, to not reading the instructions carefully, and in part to a somewhat misleading picture in the instructions.  My unit will not pick up the muzzle blast to trigger the radar when set up as shown in the picture in the manual; with the unit placed directly along side the muzzle.  I have to place it ~ 6" to the side, and maybe 4" in front of the muzzle.  Even then, I usually keep the trigger setting on "2" (i.e. 2nd most sensitive setting).  You'll want to be familiar with both the trigger and sensitivity settings in order to tweak the setup at the range, if necessary.
Also, I picked up an inexpensive 1.25" bushing/ferrule at Lowes, which I glued directly onto the aiming "V-notch" at the top center of the unit with 100% silicone rubber.  I don't remember the exact diameter of the hole through the bushing, maybe 5/16" or so, but it's much easier to sight in on your targets looking through the bushing as opposed to the notch.  Good luck!