Personal experience. I've used them on lines and in stone formations. There's definitely a very high level of energy. I haven't actually taken exact measurements, but that's an interesting point to be looked into further. I believe that those who erected our megalithic structures were fully aware of earth energy currents/fields and how to use them. I've done a certain meditation inside circles on occasion and you can feel the very powerful energy field. On one occasion I had to stop because it became quite overwhelming.