I've got a Cen Tech also, nothing fancy but it does all I need it to. After the first I was curious, so I bought 4 more of them and did a comparison. I found that they varied in sens, from 3/4" to just over 1 1/2", I kept the two best and returned the others. I saw somewhere that there was an internal trimmer pot for the gain, I never opened any of mine. Been using the first I purchased for almost 2 years now, only problem was the tip came loose, glued it back with a poly adhesive which also water proofed the shaft.