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Do The Arrows On Reference Marks Point Exactly To


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I'm looking for a rather difficult benchmark - been there twice already. Seems to be buried at least 4" down. I've found one reference mark and managed to figure out the distance from the reference mark to the benchmark. I assume the arrow on the reference mark points EXACTLY to the benchmark?


Anyone help me out on this? It would save me a lot if digging.



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It is supposed to point at the main mark, but I think I recall someone pointing out how they saw a case of an error in the pointing. I bet it typically isn't more precise than 5 degrees, but I don't know.


I'm assuming that you used the 'box score' if one exists for your PID (you didn't tell us what PID it is) to enable you to figure out how far the reference mark was from the main station. The 'box score' also gives the true-North aziumth from the main station to the reference marks. If you go to the website that gives the difference between true-north and magnetic-north for the locality of your PID, then you could also use a compass to find the direction if you have an fairly precise compass.


Another possibility is to use the 'box score' to try to find another reference mark. If you can find 2 reference marks and know the distance from them to the main station, you have, by distance measurements, only 2 possibilities of where the main station is. The idea here is that if you find 2 ref. marks, you don't need any direction (azimuth). (If you have 3 ref. marks, there is only one possibility.)

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BDT and Holo both make good points.


If you think you have the correct distance to the station from the Reference mark, then try this.


Have someone hold the end of a tape measure over the Reference mark. Have them guide you in the pointed direction shown on the ref mark at the appropriate length away to probe the ground with a thin rod on a radius in the area where the station is believed to be. We call this using a swing line.


The Monument will be roughly a foot in diameter. When you hit something hard with the probe in a few places at the same depth over about a foot or a little less, then are able to probe deeper on either side, then you will have likely found it. If you find nothing, stick to the length a bit longer and widen your search arc. If nothing , then try going both sorter and longer on the arc by 1 foot increments, Maybe a little less. I probed an entire 15x 15 area once to find a mark. In my case the direction was fine, the length to it was either improperly measured or written down.


Start with that and I hope you come up with the find!


Good Luck, Rob

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Thanks for the replies and help!


Yes, I found the distance and azmith in the box score on the original data sheet. The PID is RD3106. I now have a distance from two know points (RM 2 and the stone park building) so finding the benchmark should be relatively straightforward. I'l try to find RM 1 as well. RM 3 and 4 were either removed or have erroded off of the edge of the bluff. The current fence is about 3 feet west of RM 2. Wish me luck.



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Saw an RM recently that was easily (by eye) 5 to 10° off being direct to the mark. Of course it WAS a USGS mark / station (Towne Peak, just west of Death Valley), not NGS! All the discs were in bedrock / large non-movable boulders, so not like it happened after the fact. Just not very accurate work. Shame.


It there an NGS or other professional standard for setting RM's?

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Congrats Dale,


Nice going!




Just about everything in Surveying is done to some standard or other, it is one of the most annotated and micromanaged professions around, but for good reason. Unfortunately this procedure with respect to Reference Marks is likely nested in a 400 page book. I have seen it but I have not recalled where. If I cross paths I will Bring it here.




Mike, Do you recall off hand where the procedures for properly orienting Reference Marks is located? You have so many good things in your stash, I just wonder if you do. :-)



Edited by evenfall
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