Tuning a Dowsing Rod

I have seen dowsing rods with a well or chamber in which you put a sample of the element or substance you are searching for...the idea being that of sympathy/resonance as in like attracts like so these comments and instructions were worth posting;

"If a piece of the same wood as that of which the rod is composed, be placed under the arm, it will totally destroy the operation of it, except in the instance of water, for which any rod, they say, in any hand will answer; or if the least animal thread, as silk, or worsted (wool), or hair, be placed on the top of the rod, it will prevent its operation; but if a piece of the same animal substance, or of the same wood as that of which the rod is made, provided the rod does not answer, be placed under the arm, it will cause the rod to rotate.

If a piece of gold be held in the hand and touching the rod, it will prevent its being attracted by that metal or by copper, for the rod will be repelled towards the face; or if iron, lead, tin, silver, limestone, bone, or coal, be held in like manner, it will also be repelled, and vice versa.

If a person with whom the rod does not naturally operate, hold a piece of gold in his hand, the rod then answers to gold and copper; and thus with respect to the other metals and substances; and upon these properties of the rod depends its power of distinguishing one metal or substance from another.

Another mode however, grounded upon the same principles, is pointed out as being much more ready and certain, viz. by preparing rods that will ONLY answer to some one of the aforementioned substances. The mode of preparing them is by boring a small hole in the top of the rod, and by putting into it a very small quantity of each substance, except that after which search is to be made; the hole is then to be stopped up with a piece of the same wood of which the rod is made."