I used one a lot way back when. The trick is you have to know where the point is first. That sounds silly but actually it's not. You get near the corner then use the dip needle to find buried treasure. They really work quit well once you got the hang of it.
Fast forward a few years, the new electronic "pin finders" come out but are expensive and I wouldn't buy one until the price came down (dumb idea) of course that didn't happen and I finally bought one and learned that I couldn't work with out it. Last time my pin finder broke I just packed up all me gear drove to a friends office and borrowed his spare until mine was fixed. All of my control now has a magnetic signature so point ties etc. are not necessary, just wave your magic wand near where the control is and bang, there it is. It is really amazing how our work patterns have changed over the years to fit the technology that has grown up around us. I still know how to do it the old way, but who would want to.
T.W.
I used one when I first started surveying. Very frustrating. I still have one.
We used one when I was a neophyte. When it worked and you found something you puffed out your chest and pretended you were hot stuff. When it didn't you strung together expletives at a loud volume. It often worked better if you knew there was something located where you were looking...
A friend who knows I like that kind of stuff picked one up for me at a garage sale for $5.
At first glance there are two problems The leather strap has been cut off the case, probably because it broke. And it tends to point down regardless of how I turn it in midair.
I think I need to open it up and move the weight on the needle. Is that a standard operation? Maybe it came from different latitudes?
Does it point down with the pivot vertical so that the needle moves in a horizontal plane? Or does it point down with the needle oriented north-south and moving in a vertical plane?
I last used one for finding irons about 1964. But with the needle moving in a vertical plane, it always does point down to some extent. It's something about the earth's magnetic lines of force being at an angle to the ground.
If the needle is oriented north-south and moving in a vertical plane, and if it dips to something like 50 degrees below horizontal, I'd say that's normal for this part of the country. And the dip angle will stay the same when the instrument is moved around--unless you're near an iron or other magnetic object.
To find an iron you move it around and find a place where the angle changes. If you're south of the iron the angle might get flatter. If you're north of the iron or on top of it, it might go up to something like 80 or 90 degrees below horizontal. You have to be pretty close to the iron, something like 4 to 6 inches horizontally, and the iron can't be buried too deeply.
I remember using the long strap to hold the instrument just above the ground while walking around, keeping the instrument oriented north-south, and watching the dip angle through the built-in mirror.
One popular use for these was to find cast-iron water valve boxes. I didn't do that myself, but heard about it. The valve boxes would affect the dip angle quite a bit since they were a big piece of iron, and the dip needle would find them pretty easily.