As you can see, most people use the WAG method. In all realistics, if you don't use some sort of data recorder that uses a GPS or something to measure dist acurately, you won't be close. I have had people call the tower many times when I am doing jobs over town and they always say we are 50 feet above their roof. The tower usaully tells me about the call, but I am on radar and am at between 1000 and 1500 usually.

Very very few can accurately judge distance when it gets more than a few feet from them.