Sometimes it of use to know the distance between yourself and a car another person and the like. Take a few minutes to do this and you will have a tool to approximate this distance. Your hands have a fixed distance between this finger and that and a fixed distance to each finger and knuckle. In a place where you know the distance like a running track or a range (Just count how many steps you take in 100 meters and you can do this anywhere) Now see how much space does a full man take as you look at him. Perhaps two upper knuckles of the pointing finger or something else. Once you do this and stay carefull as you chop wood, you will be able to know that distance.