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Magnetic station disk


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Last weekend I foundGG0638 on the Univ. of Arkansas campus in Fayetteville. What did I find? Is it used differently than other benchmarks?


BTW within a few square yards there are a altitude benchmark, a HARN disk, a triangulation disk and this magnetic disk. The North and South towers of the Old Main building are also listed as benchmarks. How many other places have such a high density of benchmarks?

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Good picture.


Purely as conjecture, I think that a magnetic station disk would be used for one of two things. Either this is a place where a surveyor has calculated a specific magnetic north bering compared to a polar north, and can be re-used as a reference as magnetic north shifts around, or this benchmark is used as a local reference for a magnetic anomally in the area. One of the pros around here may be able to give you a better bit of information.


In places wher there is a high concentration of Iron, Nickel, or other magnetic metal, it is not unusual to find that the local North varies from standard Magnetic North. This is one of several reasons that Magnetic North is not used by surveyors.


The top of the IDS building in Mpls has five benchmarks alone. Two building corner beacons, Two tower beacons (one of which is currently inoperable), and a benchmark in the center of the roof. Since I don't have approval to walk around on the roof, I don't think it would be right to claim the last mark.


As local construction changed the landscape, or skyline, benchmarks were added for usefulness. Also as different types of projects were started or in progress, different types of benchmarks were installed.


Look through the message history and you will even find benchmarks that were physically placed on top of each other.


Have a good time.



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There are magnetic observation stations all over the world, where a magnetometer is used to measure the earths constantly changing magnetic field and magnetosphere. NGS once had a program called the geomagnetism project, but I think it has been replaced by more modern programs. The cluster of markers of different kinds in one small area is fairly common for research and training facilities such as universities, where students of engineering and geodesy use them to practice.

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As you probably know, some colleges and universities have very extensive engineering programs, while others have few if any, so some campuses will have a lot of markers while others may have none. Some of the very best programs are at small schools in out of the way places like Big Rapids Michigan, Carbondale Illinois, Lehman Pennsylvania, Kalispell Montana, Johnson City Tennessee, and Marietta Georgia.

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