Right, why is 250 ppm bad (red), and 125 ppm good (green)? Or is it that the camera can't focus closer than 5m distance? Doesn't seem related to installation

Right, why is 250 ppm bad (red), and 125 ppm good (green)? Or is it that the camera can't focus closer than 5m distance? Doesn't seem related to installation height, but that's another consideration.