I put a flat blck peice of steel down at the hundred yard mark laying flat on the ground, if I look at it with the spotting scope and can see the heat waves riseing I look for the amount of distortion if there is much I shoot in the morning or evening, its on old bench compitition shooters trick. It can be frustrating to have this problem, those heat waves at the time of year when its cool at night and warms very fast during the day can cause an optical illusion that will cause added problems beyond what you would expect for things like glow type sights, I have seen it so bad that the target appeared to move when a breez started up. Lee