"I am certainly not deluding myself in any way, and you have no proof to the contrary"
That's a bit rich, asking ME for proof when you are the one who has presented extravagant claims without offering the slightest shred of proof. What I said was, "Nothing that you've presented here suggests anything beyond the possibility that you are deluding yourself either deliberately or without realising it." That's a statement of fact, based entirely on your own words and as such does not require proof.
You seemed to miss the point I was making earlier about your measurement being exactly 13 inches. Imperial measurement is an arbitrary human invention and it's extremely unlikely that a natural phenomenon would work to "exact" measurements. Your 59'7" confirms that you are claiming a high degree of accuracy. If you had decided to use a metric tape, I suspect you would have claimed the measurement to be exactly 33cm. That would also have been very close, but would have been about half an inch different at 60'. It's the fact that you are so adamant about the exactness and the significance of the numbers that suggests to me that you are likely to be fooling yourself.
"Unless you are prepared to give dowsing a fair trial, either by sticking at it for a while, or considering that so many do find that it works, then because nothing physical exists to prove it, do you just then dismiss it?"
I don't dismiss dowsing. On the contrary, I have successfully used it to find lost drains. What I am calling into question is whether the results you are getting and the interpretation you are putting on them are justified or whether you are merely the victim of your own eagerness to find something.
The whole point about dowsing is that it relies on a device (bent rods, hazel twigs, whatever) that is essentially a hair-trigger. The slightest movement of the dowsers hands causes the device to register something. Now it may be that the movement is caused by some unknown extraneous force, or it may be the result of voluntary or involuntary movement caused by the dowser's own brain and the two are very difficult to differentiate even by the dowser himself/herself.
Several times in the past I have looked at drawings made by dowsers of their findings at various ancient sites. I have also done some dowsing myself at such sites and I have to say that the results you describe are far more elaborate than any others that I have encountered. If the patterns were "genuine" then one would expect reasonable a reasonable concensus of dowsers to get similar results.