This is my normal background at the lake bed, photo is of Rick Stubs with one of his UpRoars last week. That will be another story told! I used my TNC that day. It doesn't care about the background very much. In this light and background I do need to be closer to the prop, with grass or asphalt as a background I can stand 4 feet behind the prop and get good readings. That's what 100 bucks will get you. Other tachs are more sensitive to the different light and backgrounds. Most of my glow engines are YS and I have discovered they all seem to like to be 500rpm fat at the top end. I can hear the drop but the tach shows me exactly how much. Once I tune one of my engines I don't change the needles for about 6 months when the weather changes a lot or if I change the prop size. Tachs come in handy but not often enough to spend the big bucks on one. I needed one at one point so I have a good one but it isn't used much these days.