SAMPLE DATASHEETS

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PID - (Permanent Identifier)

Station Permanent Identifier (PID)
Always displayed
The PID is also found on the left side of each datasheet record.
The PID is always 2 upper case letters (prefix) followed by 4 numbers.
EXAMPLES :
PID = MY1234,
MZ5678

NEW ENGLAND PREFIX MAP

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DESIGNATION

Each benchmark has a name, called a designation, with no set format.
It could be JONES or E 37 RESET or WASHINGTON MONUMENT 1913.

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REFERENCE MARKS

Reference Marks (RM) were set to assist in locating the Triangulation Station and also to help determine if the Triangulation Station was undisturbed in its original position. The measured directions and distances to them could also be used to reset a station mark if required. Reference Marks were factory stamped with “REFERENCE MARK” and with an arrow used to point in the direction to the Triangulation station. The original surveyor stamped the RM with the name of the Triangulation Station plus the number of the RM, just prior to setting. For example, the first RM for station JONES would be stamped “JONES NO. 1 1936”. The surveyor measured the direction and distance from the triangulation station to the Reference Mark (RM) and recorded the information as part of the station’s description. Later, if a surveyor attempting to find a Triangulation Station stumbled upon a RM first, the arrow and the published distance and direction between the RM and station would be valuable aids in the station recovery. To check the position of the Triangulation Station, the new surveyor could measure the angles and distances to the Reference Marks and compare them to the original values. USC&GS specified a Reference Mark as early as 1913. By the 1920’s, two Reference Marks per Triangulation Station were specified. Reference Marks were usually set within 30 meters (one tape length) of the station. Reference marks were numbered clockwise from north and set about 90 degrees apart. If a RM was destroyed, a new Reference Mark would be set using the next consecutive number. The disks would be set in a concrete monument buried in the ground, or set in a drill-hole in a large structure or bedrock. This type of disk was used from about 1913 to about 1970. Although the distance and direction provided enough information to compute the positions of the RMs, it was not standard procedure to compute them. After about 1970, National Geodetic Survey REFERENCE MARK disks were used.

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AZIMUTH

A TRUE NORTH, PRECISE COMPASS READING 0 - 359 (DEGREES)
Azimuths are always TRUE NORTH readings unless it says otherwise.

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AZIMUTH MARK

An azimuth mark, together with its associated triangulation station, provides an accurate azimuth (like a compass direction) that is based on true North rather than magnetic North. This azimuth is used to orient local traverse surveys. These marks also have arrows in their centers that are supposed to point toward the triangulation station.

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BOX SCORE

On some NGS datasheets (usually the ones for triangulation stations), there is an area of data enclosed in a box made of dash characters and vertical bar characters. Inside this box are distances and azimuths FROM THE PID (MAIN STATION) to other stations, reference marks, or azimuth marks.When it exists, the box score information is extremely useful for finding the main station from its reference marks and vice versa.

Distances given in the box score are meters, to convert meters to feet multiply by 3.2808

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TOOLS FOR BENCHMARK HUNTING

What you need on any particular hunting trip depends on the kinds of marks you plan to hunt for and the type of terrain where you will be hunting.

BASICS:

DATASHEETS
MAP
TAPE MEASURE
COMPASS
CAMERA
RAGS OR PAPER TOWELS
SCREW DRIVER OR PROBE
TROWEL
METAL DETECTOR - (OPTIONAL)
GPS RECEIVER - (OPTIONAL)
If you like to find marks that are off the beaten path you will need a
BACKPACK

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FINDING THE MARKS

A GPS receiver is a great tool to get you to the general area where the mark is located, ( 15 to 50 feet) for adjusted coordinates, and can be 100 feet or more for scaled coordinates. When your GPS says you are there, put it away, it is useless for finding the stations. Now use the description from the datasheet, try and locate the landmarks in the description to measure from. Triangulation stations usually have reference marks associated with them. NGS recovery reports of triangulation stations involve looking not only for the principal mark, but also for any associated reference and azimth marks. Usually at least one of these is fairly obvious and that will give you a start on finding the others.The measurements between the triangulation station and the reference marks are almost always given in what's called the box score. The box score gives the true North azimuth from the triangulation station to each reference mark in the format Degrees Minutes Seconds (dddmmss.s) but using just degrees part is sufficient for hunting. It helps to have a sighting or mirror compass that reads to the nearest degree.The mirror allows you to view the compass dial and the background at the same time, which makes mirror compasses better for taking accurate bearings. With a baseplate compass, you can not view the compass dial and the target at the same time,  
You need one mark to find the rest, it does'nt matter which one you have to start. Secure one end of the tape measure at the mark, use your compass for the general direction you want to measure,once your at the right measurement, hold the tape with one hand and compass with the other. Sight your compass at the mark, move left or right until you are at the correct azimuth, if the tape measure is in a straight line and the correct azimuth, you will be with in a few inches of the mark your looking for.
 Usually reference marks are more or less at right angles to each other with respect to the triangulation station.
If you're looking for a reference mark from the triangulation station, use the azimuth from the box score. On the other hand, if you're trying to find the triangulation station from a reference mark, you need to convert the azimuth to the opposite direction using the following simple rule: If the azimuth is less than 180 degrees, add 180 degrees, otherwise subtract 180 degrees. Or you can just BOX the SOUTH end of the compass needle, which gives you the same results without the math.
Azimuths in a box score are in terms of true North. Your compass points to magnetic North instead. To convert from one to the other, you must get the declination and use it. Most sighting compasses have adjustable declination, once it's set you don't  have to add or subtract the declination value each time you sight a bearing.
 The declination is different everywhere on Earth and changes as time goes by, so you will need the current local declination at the approximate position of the triangulation station.

DECLINATION MAP

On some datasheets in the discription, the compass direction from the reference marks to the main station are given in the
QUADRANT FORMAT
In this method the compass dial is divided into four quadrants, namely NE, SE, SW, and NW. North and south are at 0 degrees, and depending on the quadrant, angles (up to 90 degrees) are measured away from north or south (whichever is nearer) towards East and West directions. For example since Northeast (NE) is 45 degrees towards east of North, using quadrant notation it would be N45°E (read North-45 degrees-East). Similarly NNW is equal to N22.5°W. ESE is S67.5°E.

 
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Click to find NGS Benchmarks in your area.

Don't forget to get Land owners permission.

GOOD LUCK !

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