Rodney Weaver was a great believer in dowsing - though not in other forms of esp. They did work - he made them from welding rod (if I remember correctly) but held the "handle" end inside copper tube, thus allowing them to move freely without his fingers touching them. He used them successfully to follow drains, watercourses, electric conduits, pipework and similar underground features. At Oakeley, in Hollands Upper Mill area, he did several traverses across the area, and successfully found the alignment of a major water supply pipe which was invisible on the surface - we only verified the location afterwards by digging ! Why he was carrying them undeground on that particular day, I don't recall. I tried using them, and although, to my surpise they worked for me, they didn't work as well as they did for him.
Grahami
The map is the territory - especially in chain scale.