Benchmarking 201: Locating and Logging Benchmarks

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Benchmarking 201: Locating and Logging Benchmarks

Postby GrizzFlyer » Wed 2007-01-31, 00:56:36

If you are thinking about dabbling in or getting a little serious about hunting benchmarks, this article may be of some use to you. It is intended to be for your assistance only, to help you to avoid some common mistakes, and to be used as a guide until you develop your own benchmarking methods.

-FIRST of all, you need to read a Benchmarking Hunting article and a Benchmark Hunting forum topic on Groundspeakâ„¢. These two items will answer many of your questions regarding benchmarking.

Benchmark Hunting article:

Benchmark Hunting forum topic: ... try1811674

NEXT, read the Benchmark 101 primer on this NWOGEO website which gives you instructions on how to download benchmark information from the National Geodetic Survey (NGS). Most of it should already be familiar to you after reading the article and forum topic above.

Benchmark 101 primer:

- READ the page for the benchmark and any entries that may have been made by previous finders. Many times they will have useful information.
- READ the NGS data sheet descriptions and previous official entries and understand what they are saying by picturing the situation while you are at the scene. Take into account the year those entries were posted. Many were in the decades prior to and after WWII, and many physical attributes have changed since then.
- DO NOT rely on log entries of "Mark Not Found" if they are from the US Power Squadron. They are many times inaccurate.
- DO give considerable weight to log entries of "Mark Not Found" or "Destroyed" if they are from local or state highway departments, local surveyors, or the NGS.
- eliminate entries in your personal database/files that have been positively identified as being destroyed. No sense trying to find something that isn't there.
- GPS coordinates: Don't rely on the given coordinates on the majority of older (pre-GPS) benchmarks. Originally, benchmarks were meant to be located by using measurements from physical reference points, such as buildings, poles, culverts, signs, rails, highway centerlines, and so on. The GPS coordinates were later determined by a person using a detailed map of the area, and making physical measurements from these maps to obtain/guess a set of coordinates. This is called "scaling". Quite often these coordinates are inaccurate, so beware of coordinates from any benchmark if the description says they are scaled. In later years, coordinates were determined by the use of expensive GPS units, and were then listed as "adjusted" coordinates. Adjusted coordinates are almost always extremely accurate.
- Some of the newer benchmarks that are in the NGS database may not be in the database. This is because is using a NGS database from 2001.

- Wear the proper safety equipment. Some recommended items are listed in the Benchmarking 202 -Equipment file. Wear or use whatever safety equipment would be appropriate for your location and activities.
- Be aware of your surroundings. This is especially relevant when near roadways. Locating a benchmark just isn’t worth being struck by a vehicle. If you're hunting a benchmark near a railway, be aware of special dangers such as hidden objects on the ground or in the air. Railways are dangerous places Don't trespass onto railroad tracks, or railroad property.
- If there is any doubt or question about your safety when recovering a benchmark, go on to the next one. There are plenty of them out there.

-Streets, highways, and bridges: A large percentage of benchmarks are along public right-of-ways. Great care must be exercised when seeking benchmarks located on roadsides and on bridges. They are physically dangerous places, and bridges have become objects of increased sensitivity.
-Private property: Often benchmarks are placed on private property. Many people are sensitive about strangers walking on their property, and most really don't like anyone digging up their lawn or walking through their crops to get to a benchmark. Either obtain proper permission, or move on to the next benchmark on your list.
-Airports: Almost every airport will have 2-4 benchmark stations on their property, and these are usually alongside taxiways and runways. It should go without saying that you should not seek out these benchmarks unless you have some very special contacts at that airport.
-Railroads: A great many benchmarks listed in the NGS database are on railroad property. Railroad property is private property, and a dangerous area. Many of the benchmarks are on abandoned railroads, so use good personal judgment for those situations.
-Water tanks and treatment plants: Some benchmarks are located on city water tank footings, and concrete retaining pens at water and sewage treatment plants. If the area of the water tank is not fenced and not posted, and is on public property, it is probably OK to quickly locate and photograph the benchmark. Treatment plants are generally off-limits, with most being fenced because they can present a physical danger, and due to increased sensitivity brought on by recent events.

- Benchmarks that are metal disks, which includes most of the benchmarks, are identified by stampings on the disk face. The NGS database entry for each benchmark will tell you exactly what should be stamped on that disc. This also applies to benchmarks that are on a pipe cap. If you have found a disk with some other stampings, you have not found the disk you seek.

- Reference Marks. A common mistake is locating a reference mark disk and thinking that is the actual station disk. Most reference mark discs will be stamped with the same name and many times the same date of the disk you are looking for. They may also contain a stamping such as "REFERENCE MARK 1" or "RM 2" or NO. 3" in addition to the regular stampings. Many will also have a large arrow on them pointing to where the main benchmark is located. Do not confuse a reference mark disc with the main benchmark disc with which it is associated. Some reference marks are benchmarks in their own right, and are listed in the NGS database as such. You can log both benchmarks (and sometimes 3-4) if you locate and photograph them. Loggable reference marks will have their own separate PID's (Permanent IDentifier).

- Reset Benchmarks. Benchmarks occasionally are either destroyed or deliberately removed, and a new benchmark disc may be set. It can be on the same exact spot, or moved a short distance away. The new disc will usually have the same name as the original disc, and may have either a number added at the end or the word RESET added to the original name, as well as a new year. An example would be a benchmark placed in 1947 named HARRIS or HARRIS 1947 that gets destroyed or needs to be moved, and the new benchmark is placed in 1980. The new name would be HARRIS 2 1980 or HARRIS 1947 1980 or possibly HARRIS RESET 1980 or HARRIS 2 RESET 1980. Be careful to log the correct benchmark, as many times the original destroyed benchmark will still be listed in the NGS database. The reset benchmark always gets a new PID.

- Benchmarks in monument boxes. Quite often a benchmark is placed where it must be protected. This usually occurs in roadways. You'll see them all over northwest Ohio and many other places, usually right in the center of an intersection. This presents several problems for benchmark hunters. First of all, most of these benchmarks you see in the roadway are not listed in the NGS database, so they are not loggable. Secondly, they present a safety hazard to anyone attempting to read and photograph the benchmark inside that monument box. Thirdly, many people don't actually open the monument box to make sure that what they are seeking is inside. Read the NGS station description! It will tell you if it is inside a monument box or not. Most benchmark purists take the stance, and understandably so, that if you didn't actually see the benchmark, you didn't find it and should not log it as such. I've made that mistake in my early benchmarking days, and subsequent checks of the interior of those monument boxes corrected that. The purist stance is validated when somebody logs a benchmark as found when only finding a nearby monument box, doesn't check it, and the correct benchmark is actually 40 feet away at the side of the road. Sometimes monument boxes will be stamped on the flange with the benchmark name and the year. If the station description says that the benchmark is in a monument box and the flange is stamped, and that benchmark name is the same as the flange stamping, and if it is clearly visible on the outside of the monument box, its my personal opinion that a photo of the outside of the box clearly showing the proper flange stamping is close enough. Again, the purists will not agree with that point. However, I have found some stations where the actual benchmark disc is not stamped with the station name, and only the box flange was stamped. Also, many flange stampings are very faint and unreadable, so a look and a photo of the actual benchmark would be necessary in those cases. You must make the decision that your Found claim is adequate and proper.

- Benchmarks in Berntsen tubes. Some benchmarks are set in a PVC or steel tube/pipe, and then this pipe is sealed with a Berntsen cover. Here is an example of those covers: ) Most can be opened by hand or with a screwdriver. I've seen straight, Phillips, and a tamper-proof Torx with the little projection in the middle type of screwheads used.

- Intersection Stations. Most intersection stations are tall objects that can be used to determine a distance and/or angle from a long distance away, usually miles. They are commonly large tanks, church steeples, radio towers, standpipes, grain elevators, tall buildings, etc. These benchmarks (technically not benchmarks, however since lumps all NGS entries into the benchmark category, we will too) can be claimed as a find by locating the object in question and taking a photo of it, or two, if your camera has an adequate zoom capability to capture the object at the top of the structure. Although these are some of the easiest benchmarks to log, a common mistake is to log a replacement water tank instead of the original one that has been dismantled. Read the NGS description!!

- Monel-metal rivets. Used mainly by the various railroads from 1905 to about 1935, monel is a metal alloy that is about 65% nickel with the remainder being mostly copper. As such, it is very hard and highly resistant to rust , tarnishing, and corrosion. While a monel metal rivet used as a benchmark is usually not marked, they stand out from other rivets and can be easily identified. Here is a good discussion on monel metal rivets, including a couple of photos: ... 37203.html

- CORS and CORS Phase Centers. CORS stands for Continuously Operating Reference Station. It is a small antenna that receives the GPS signals and detects any changes and corrects radio signals for surveying equipment. They are usually a flying-saucer shaped or domed shaped metal antenna, and sometimes are small arrays with vertical elements. These are found mainly at the various ODOT garages and sometimes at airports or a governmental facility such as a Coast Guard station. To log a CORS site, only a photo of the antenna is required. There are usually two stations at each CORS site, both are loggable.

Here is a short discussion and a photo from the Groundspeak forum regarding CORS: ... 37203.html.

Here is another: ... 36&hl=cors

And here is one more: ... pic=147763.

Examples would be DF9324 and AJ7198 in Seneca County. Many CORS stations are comparatively new listings in the NGS database, which are not listed on

OK, you've downloaded the NGS data, loaded up your GPS and PDA, gathered all the equipment for the benchmarks you'll be hunting, and now its show time! Try to pick a few that are introductory level (as in real easy…). Just as in geocaching, let your GPS unit guide you to the area. Make sure you read the NGS data sheet for each benchmark so you know what you are looking for. The important parts are usually in the last half of the data sheet, and they will include the sections on Marker Information, History, and Station Description. There is a lot of other info there, however these three sections will be the most useful on your benchmark quests.

For most members of the Northwest Ohio Geocachers, the downtown Perrysburg area is a real good place to start. It has a bunch of easy ones that offer a variety of station types and locations. They have benchmarks on buildings, benchmarks on a water tower, and a few in the ground. The one in the lawn of the library (MC0679) is a good one to start with. Although it doesn't have a witness post, that shouldn't slow you down, as it is really easy. Find the benchmark station, verify that the disc says what it is supposed to say according to the station description, and take your two photos. Then move on over a couple of blocks and locate the benchmark at the former post office (MC0680). After that one, there is another one a few blocks to the east, it is also on a building (MC0681). Then hit the one on the water tower footing (MC0678) southwest of the library where you started. You just knocked off four easy ones. Now you can log them and upload your photos.

Many benchmarks will be slightly under the ground surface, and may be difficult to find even if there is a witness post nearby. Once they are located by probing, by metal detector, or by moving a small amount of dirt, they must be exposed enough to positively identify and take a good photo. Use your plastic putty knife to move as much dirt as you can to the edges of the station. Make sure that the markings on the station are readable. You may have to use your wiping rag and/or a squirt of water to clean it up for the photo. The inscriptions may be enhanced by using a small amount of powder or chalk. After you've taken your two photos, leave the benchmark as you found it, including recovering it with any material you moved. Make any notes as necessary and then examine the NGS data sheet for the next benchmark on your list.

As time goes on and you are exposed to more and more benchmarks, you'll realize that there can be many challenges in benchmark hunting, it is only what you personally decide to make of it.

- Found: When composing your log entry, attempt to set an example of professionalism by using accurate attributes of both the data offered and the language you use to describe it. Entries such as "Yep, its still there" and "just cruising around and I saw this" could be better worded to reflect an enhanced sense of professionalism and pride in your work, as well as lend increased credibility to your findings. It is not only geocachers that read these logs. Some professional surveyors also use them to check benchmarks. You don't have to write a story, as a simple "Station recovered as described in good condition" or similar phrase works well for a standard, non-eventful recovery.
- Note: Most stations not found would be reported as a Note if you made any kind of proper search, and found physical references present, such as a witness post or camera target. Post in your log what you did find, so that others may have access to your experience.
- Did Not Find: Log as a DNF only if you could not locate any sign of the station, after conducting a diligent search of the area using both GPS coordinates and measurements from physical references in the station description.
- Destroyed: Be VERY careful about logging a station as Destroyed unless you have proof positive that the station has been destroyed. If in doubt, log as a DNF or as a Note. A Groundspeak forum thread on station conditions, including the official word from the NGS, is located here: ... pic=147853.
- Adding Accurate Coordinates: Often benchmarks are located only by measurements from reference objects as stated in the original descriptions and any subsequent updates. As a general rule, if the coordinates listed are close enough to enable you to locate the benchmark without any difficulty, then listing coordinates in your log would probably be unnecessary for our purposes. If listed coordinates are misleading or are in considerable error, then log the coordinates at which you located the benchmark. Please take an accurate reading, as others may rely on your data in the future. GPS coordinates of benchmarks should be listed in your log if the original coordinates are inaccurate by a large margin. I have found benchmarks in which the given original coordinates were off by more than 1500 feet, due to scaling (see Reading NGS Data above). Here is an example:
- Station Description: If physical attributes used in the station description have changed significantly, then post this in your log. Examples would be buildings that are no longer there, roadways relocated, fences taken out, bridges rebuilt, culverts missing, and so on. Also note if there is no witness post present, if the last station description says that one was present. They help immensely in quickly locating a benchmark location. You may get a handle on the proper language by reading a bunch of NGS station descriptions and understanding how professional benchmark installers and users compose station descriptions that are accurate and understandable.
- Photos: There is no absolute requirement that photos be taken to log a benchmark. However, it is strongly recommended that you take at least 2 digital photos when recovering a benchmark, and post them with your log. One close-up should show the face of the benchmark in detail. This close-up positively identifies the benchmark for others to see, and establishes beyond any doubt that you found the correct benchmark. The second photo should show the overall landscape of the area, making sure the benchmark location can be accurately determined in your photo. This landscape photo would assist benchmark hunters following you to locate the correct area. Some benchmark hunters use an image editing program before they upload a photo to their log, to insert a marking to show exact location of the benchmark if it is not readily located in the landscape photo. Some also place the benchmark PID in a corner of the photos.

8: LINGO (not described above)
- PID: Permanent Identification number. Each station is issued a PID to identify it. The PID is not the station name inscribed on the station.
- Camera Target: Material used to locate survey markers by aerial photography. They can be a large circle of concrete or crushed stone surrounding the station, crossed lines made of white lime, white painted crossed lines on roadways, etc.
- Witness Post -Carsonite and fiberglass posts, metal posts, wood posts. Vertical objects that are placed near the survey marker to assist others in locating it. While usually placed a foot or so from the survey marker, but they can be placed much further away. Read the station description for witness post placement.
- Chiseled Square: Just like it sounds, a square made by chisel in stone or concrete, sometimes in metal.
- Keel mark: A temporary mark made with chalk, pencil, or marking crayon. Sometimes they are made semi-permanent by a chisel mark. Very, very few benchmarks will be a keel mark.
- Rail: A measurement used by various railroads to indicate a distance or length. Most rails were made in 39 foot lengths, so 3 rails would be 117 feet. However, some railroads used shorter length rails, so their distances stated in rails would be shorter.
- Monument box: A cast metal box, usually square, that covers and protects a survey marker. Usually all you'll see is the very top, consisting of a flange and a heavy lid. Most have a pick hole that can be used to open the box, some have a security bolt that must be removed. Opening the box will reveal the benchmark. Sometimes they are called a Neenah box after a large manufacturer of such items (usually a #1976 or #1978 box).
- PK Nails: The PK stands for Parker-Kalon, and are a hardened zinc-coated masonry nail often used by surveyors to mark a specific point. PK nails are usually used in roadways and on utility poles to be used as a measuring point to a benchmark or another measuring point.
- Shiner: Usually termed as "a nail and shiner". They are a round metal or plastic washer with a small hole in the middle, and are used with a nail to mark a specific point as a measuring tool. They are almost always used in posts, utility poles, or sometimes trees. Charter Member
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