[time-nuts] USGS Benchmark accuracy...?

Majdi S. Abbas msa at latt.net
Wed Sep 14 17:07:22 UTC 2011

On Wed, Sep 14, 2011 at 08:39:44AM -0400, Michael Baker wrote:
> Hello, Timenutters--
> There is a USGS survey benchmark on the side of the road
> just a half-mile from my house.
> Any guess as to how accurate these are?

	No guesses, but for something in the NGS, you can find
out.  However, many USGS marks were placed for USGS mapping 
purposes, and may not be terribly useful otherwise.  If it was
a well surveyed USGS mark, it could be part of the national

> The head of the marker post with the brass plate on the top
> is flush with the surface, but covered with grass.  I had to
> scratch around to find it.   There is also a second concrete post
> in the ground about 30-40 feet away--  apparently you line up
> the two concrete markers to give you a true cardinal direction.

	Unclear as to whether you've found an Azimuth mark (in
which case it's horizontal position won't be well surveyed at
all -- it's not intended as a horizontol control) or just the
witness posts associated with the primary mark.  

	If the others aren't witness posts (designed to help
you locate the reference), then this sounds like an azimuth
marker and its associated reference, which were only located
with enough precision for a surveyor to be able to find it later.

	Different marks were intended for different things
(elevation, horizontal position, azimuth, cadastral survey,

	What were the markings on the disc?  If it's part of
the NGS (and not just a USGS BM), a data sheet is available
online.  Also, where is it?

	Any pictures?


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