beam to come back and that gives you a measurement of twice the distance to the obstacle in that direction and so it's a nice way to directly measure 3d it's a little bit problematic at times because sometimes you have mirrors and then the thing doesn't come back your reflects off in another way or you might have glass that acts much like a mirror and the same thing will happen you don't get the measurements back but if you have nice matte surfaces it's a really nice way to measure how far away things are dynamics is noisy because of wheel