Those lines are probably BDC holds calibrated to a 300 yard offhand/kneeling zero. Should be able to put the target anywhere inside the funnel and be able to miss IPSC targets at 400, 500, 600, etc with anything from 55gr 223 to 175gr 308 at any velocity. Looks like it should work for both mil and moa so if your spotter calls your misses in mils you can say "what is that in minutes" and then just hold left edge and send it.