Apparently, this was used by Cdn military personnel and others for some very long shots. Wonder where the inspiration and knowledge to invent some of this stuff comes from. They range from 500-2500.00 according to the website. I saw where someone had bought and installed one, made me look it up as it seemed rather strange, once explained, it is quite the gizmo
https://www.youtube.com/watch?v=6TZDrqaLkOg