fatshot OK, that video is exactly what I'm talking about. Thanks!
I like his idea of using one stroke to calibrate from better than my idea of trying to find the stroke that goes 30 feet for example.
I learned a method from a teacher that expands on this idea. You track where a certain knuckle goes back to on the back swing. He uses a forward ball position and a piston stroke. For reference points he uses various male parts, then inside thigh, mid thigh, outside of thigh. Outside of the thigh was good for 20 paces. Beyond that you improvise. He has a rule of thumb for how much to add or take off for slopes. When I'm in practice with it, it's very accurate and awesome. I haven't been doing it this year. I'm going to start by just doing one of the reference points, like your guy in the video.