evenfall

Geo, Would you like me to scale it off a map for you or go there and survey it in person? PLSS was never Surveyed or held to Geodetic locationing. They turned angles with a transit and pulled measurements with a chain. It is feasible that I could re-accomplish the original survey with modern methodologies and find myself faced with a bit of error correcting to do. Sorry man, this is really nothing more than a guess unless the corner happens to have an NGS monument surveyed at the location. Apples and oranges for the most part. Rob

Believe Me Guys, Holo and I as well as those at NGS feel your Pain. This stuff is sometimes hard to get ones mind around and accept, but sometimes we must simplyagree with things that are not easy to understand because ultimately, what is needed is a system that works as well as it can, not a system that is unavailable for use because it is not perfect enough. Real science has warts and all sorts of details we have to observe as well as make exceptions for. It is just the way it is. It is what we have been trying to Illustrate all along. What you can know, and hopefully feel good about is that the NGS is the oldest scientific arm of the US Government. After 200 years, the work they have done is nothing shy of monumentous. They too have had to reconsider, more than once, the things they felt they could hold as truth and fact about the shape of the earth and continent. To this day, it continues to evolve. We may yet think back to this discussion and say, remember when we thought the earth was most like NAD83 and WGS84? Holo, Nice work on the Graphics. I am not sure everyone understands, but your example is right on the money. Rob

BDT, You have already been Answered. I suppose you have a right to your opinions. You're welcome. Rob

Cows are very interested in what people are doing. They love to come over and see what you are doing. An unattended tripod will be used as a scratching post as fast as they can get to it. Of course they will knock it over with the instrument on it, and step on it while not knowing any different. They may even roll on it if they think it will give them a good back scratch. Yup. They will stand and watch for an hour or two, then they will start eating and graze away in search of good eating. Unless you move then they will need to supervise that too! :-D Cows... Gotta love their company. I guess :-) Rob

DDDale, 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

BDT, We have written pretty exhaustively about this meter, I think the explanation has been repeated more than once. But maybe we are missing the best treatment of the matter. There is nothing hypothetical about the Meter or the Scale factor. I feel like I am running out of ways to explain this. but maybe this will help. I'll give it another shot. First, The Geodesist was not trying to be hypothetical either, he was trying explain to you how it really, actually is. The quotes around Meter were meant to denote that Scaling factors alter them and we need to keep that fact in mind. We are still supposed to think of the meter as a meter, as it is still the representative unit of length. It just sees a bit of alteration from the mathematical equations and it's various processes. We have to both observe it and accept that this happens to it. Ok, We have agreed that WGS84 has mathematical models which are used for it's determination. We have agreed that NAD83 has mathematical models which are used for it's determination. We have agreed that they are not the same models. Let us agree that the Meter is the reference standard Meter we all know, because All surveyed observations are the meter, and in these mathematical models, prior to the equations that make them Datum used the same meter. It is the only one we use. 2 different Ellipsoid models with different mathematical values. Both close but not equal. Lets call the two ellipsoid models X, and Y. 2 different geoid models with different mathematical values. Both close but not equal. Lets call them A. and B. Models X, and A were used by WGS84 Models Y, and B were used by NAD83 When X and A are taken together to create the WGS84 Datum, the numbers mix and integrate and due to this integration, we observe, AFTER the integration, that the meter seems to be a slightly different length than the one we used to begin with. Some part of the formula causes a scale factor to occur. This scale factor is the result from how the integrated number affects the length of the meter when looked at through a global model. It causes the length of the meter to change from forcing it to conform to the curves and shapes of the ellipsoid and Geoid as taken together. Models Y and B are going to have the same thing happen to them as they are integrated into the Datum they are meant to be. Only the factors within this particular model Though theoretically similar in method, are going to cause a Different value of scaling to occur which will be a different length for the meter as an end result. There is no Hypothetical meter. There is a real one and the effect that mathematical results from some very difficult equations cause to happen to it. Even after the fact, It is still meant to be taken as a Unit called the meter. So to your question: is the "scale factor" between WGS 84 and NAD 83 "meters" a constant for any pair of points A and B (in the U.S.)? It depends. If you are comparing the NAD as viewed by the WGS, then the scale factor comparison will belong to the WGS Framework. It will be constant within that framework. If you are comparing the WGS as viewed by the NAD, then the scale factor comparison will belong to the NAD Framework. The scale factor will be constant within that framework. They each have their own Scale factor however and they are not the same if you were to rip each one out and lay them on the table. The scale factor is a product of the integration and each system used different models so the factor would be a net result which would also be, different. As an additional thought, There is no third form of control in the comparison, against which we can compare the other two, and if there was it would suffer the same anomalies. So what would be a good reference standard? There isn't one. These are supposed to be the reference standards. The Meter as A priori is not meant to be taken as a statistical Variable. But once the Formulas are applied it becomes a statistical Variable. The Scale Factor is a product of the Statistical variable that affects the end result length of the meter as an end result. The Pair of points will never be the uniform "same due to different earth centers and which are not linear, the difference is in three axis: Left - Right, Up - Down, Front - Back, not simply the straight line distance between he two. This causes the surfaces of the Datum, which you could think of as an integrated ellipsoid-geoid, to be different in A, the three axis's, locationally, B the Geoid Model, and C the ellipsoid model, all taken at once. In the end they are different and they do not exactly share the same space exactly either. Hope that helped. Rob

Artman, Jeremy mentioned in the forum late last year that he would be interested in procuring an NGS update, but the NGS no longer makes a CD-R copy of the database available. The only way to compile Database as of right now is County by County, As online downloads. Hard to say whether Geocaching is up for that ordeal. Maybe there is a work around Who knows. With NGS keeping their data accurate on a full time basis, and geocaching having placeholders for most marks, perhaps the NGS stations which are not in Geocaching would be a better focus. Perhaps purging the PID's which have been removed by NGS from the geocaching database is also a good idea... Anyone want to take that on? As for the ontario stations, I'd have to concur with BDT, Contact Jeremy at Groundspeak and see if he is interested. It really is hard to say whether he would like the idea or not. Nothing Ventured, Nothing gained, So... Venture

Now that is what I call determination! :-D

The Meter used for Geodesy begins with being calibrated to NIST standards. All of our equipment has to undergo rigorous calibration standards frequently to remain in certification. That highly calibrated Meter definition becomes mathematically scaled as the numbers get crunched by the various factors involved. If this does not seem acceptable, well, take a math class and brush up. It does happen, and it is not avoidable. There are simply some constructs in Applied Mathematics which cannot be avoided and this is one of them. No Matter how anyone slices it. The length of a Meter is nothing more than the product of a negotiated agreement. The agreement has changed over the years and for all we know, could still. This is another construct we have to accept, because there is nothing any of us can do about it. Comparing anything argumentatively to assumed accuracy between brands of Consumer grade GPSr is similar to wanting a screen door on a Submarine. Why would we want to try to do this when in the specified reality we are truly blind when under 10 feet? We simply cant. Bill 93 took a stab at it while back and he concluded that he got mixed results with one unit over time as I recall, but he did take a scientific approach to the problem and that was very enlightening. Consumer grade gear is as dependent on the quality of the GPS Constellation as anything else, except that the Accuracy is simply untrustable under 5-10 feet. Please remember this discussion of Datum difference is dealing with lengths in the Centimeter and Millimeter range. It looks to me like re reading this thread would help some of us get back in the game and on the same page. This thread has very carefully laid it all out on the table. It is very representative of what the deal really is. We have tried to present the way it is, Not what we would prefer. In the final analysis, all the Mathematics of Geodesy become secondary to the politics of what the Geodesist decide will be the best standard for their intended purpose. They go with the best models they have at the time, which they thing will work for the purpose. It is a snapshot of that time as well. I can only imagine they are striving for the ultimate explanation too. There is no one Be all, end all solution to any Geodetic Question. Please trust me when I say as someone from the field that it is a lot to keep up with and a lot to keep in mind. It was just as much to learn and understand. It really never stops. I could get handed a new piece of gear tomorrow and a new Datum to use with it in a year. Then I have to look into what I used to believe was the best of what is thought to be true and see how it may have changed. See if there is now a better observation and explanation than what I had. It is simply just the way it is. To Add to what Dave had said, The DOD NGA, (Department of Defence, National Geospatial Agency and it's predecessors) Had nothing to do with the development of the NAD83 Datum. In the Civil field we use NGS control, we go with what they say, and they take the responsibility for their control. It is very good control. Arguably the most accurate control in the world. We do not cross compare it. It is simply not useful to do so. We could of course argue the differences until say, whenever, but what would be the point? The guy who pulls all the strings is the king and he could get up from the table and choose to say, ok, all Geodetic measurements on our system are to be transformed 3 cm to the northeast. Then we would be arguably no closer or further away that we already are, when you base it on base it on what is currently known and take the entire grid on the whole. Yet it would be the new rule. The earth is not a perfect ellipsoid. It has an ever changing Geoid. The GPS Constellation is tweeked for accuracy in real time. There are atmospheric distortions. Ground control for DGPS is meant to help curb atmospheric distortion, yet was derived from and based on the problems already considered. Then there is calibration and the laws of diminishing returns... Will we ever find the one true spot? No. See? It is pointless after a point to keep beating on it. I Hope that helps some of us sleep better. Good Luck. Rob

Geo, Whoops! SPCS, State plane Coordinates was developed by NGS, well CGS, back in the 30's for use with plane surveying techniques. Quick and dirty, the SPCS is allowed to ignore the curvature of the earth by dividing the States into Zones. As long as the zone (which usually follow along county lines, and is made up of multiple counties) does not grow too large, the flat plane can remain highly accurate. It is also very useful when used with Maps, specifically the Transverse Mercator projection, because of the straight ahead use of Cartesian Coordinates. Most of the figuring, thanks to being flat can be done with reasonably simple Geometry. The nice thing about it is that since the zones are so small, linear measurements are considered accurate to 1 in 10,000 units, with no dependency on unit type, That is four times more accurate than UTM. The grid is easy, it eliminates trig for positioning. PLSS or Public Land Survey System is primarily used for the boundary surveys of real property. It uses the Township, and Range grid system to to determine where are the boundaries actually are. You have the standard T&R, Sec, Half and Qtr layout, and so on. Parcels of land are described as to size and shape based on those sizes and shapes and the deviations from those sizes and shapes. The sizes and shapes of boundaries of land and real property were both sort of scientific and sort of legal, and were never always perfect, but the hope was always that they would be describable as possible through the use of this system. Geo, While it is true that each of these systems use a grid, so to speak, only one of them is using a mathematical coordinate system to which geometry is applied. That is the SPCS and as you know, every NGS Datasheet has SPCS positions for every PID. Though the PLSS system has an interest in being geodetically accurate, it is more an afterthought than a basis in it's design. The current managers of PLSS at BLM have expressed that they are working to attempt making PLSS a better fit with respect to geodetic positioning than it had in the past. It is something they are concerned with and that will happen over time. Rob

Bill, Last fall we had some treads on PLSS and I wrote a few posts all about it, Mike, Z15, contributed a great image which had a diagram of how the township range section and other components divvy up. In Washington, just as in the midwest, the PLSS system runs pretty square where it is easy for it to. We didn't have the metes and bound situation or a treaty, but there were rivers streams and hilly or mountainous terrain that would alter the shape of things. Based on my primary experience with that area, I tend to draw on that when I answer. I have run into my fair share of angle points in my time, but as I said yesterday, the BLM Database was down, <checking...> and yup, still is offline, so I have no way to see the maps and photographic images to speak to the specific area. There are lots of local things going on everywhere as we all know. JBA's informative post concerning the things going on in Arizona were interesting. I like learning something new everyday, that was cool to know. As a rule it will try to be square, in places it cannot so it doesn't. We go with what is on the Map and in the Survey Notes. Rob

Yeah, let's all be reminded of that the next time we fail to come to a full stop at a stop sign or recirculate a Where's George Stamped Bill! :-D

I Agree with BDT on the digital editing, it is a great way to work and you can place text and arrows in the picture where ever needed so as to not obscure the details you decide are important. Sometimes lees to carry is well, less to carry. I often put a 100 foot tape in the large back pocket of my survey vest, grab the Datasheet Camera and my GPS and go on recon. Most I'll ever need is already in the Vest. I have found that making the shot in the first place with the survey marker clearly visible is important. It is important to be able to see the station in the area pic. I have shot a few in low light where things showing up would be more difficult as well, but I have a work around. I use 25' Lufkin HV 1425 Tape measures. Seems like I have a ton of them. It is Hi-viz orange and we in the survey field like this model because the tape has inches scale on one side and feet in tenths on the other. They are about $14 at home depot and though you can get them at survey supply houses, the cost is higher. I am carrying this thing anyway so I put it to multiple use. Anyway I will take a couple shots of the station. Some are for my reference, some are for editing for NGS I often lay that bright orange tape on the station in low or bad lighting to show me where to look, then in the pic I intend to brighten and edit I can go right to it. that pic has no tape measure in it. The Hi-viz orange is really a help sometimes. then I can do what I need to to the edit and have confidence with things that are hard to see. Just use a reference pic to help edit the real one. Delete it when you are done. Holo's evidence ruler looks cool but I have another Idea. A Dollar bill is six inches long and everyone knows the size of a Dollar. It is instantly familiar to everyone. More familiar at a glance than with the scale on that evidence ruler. Why not go to the bank, get a brand new dollar and take it to the office store to get it laminated. It would be a great way to show scale at close up range, with being something everyone in instantly familiar with and the Lamination will help it be durable in all weather. I have used a dollar as a pocket tape measure many times. It would be a cheap solution and thrifty at that in terms of both cost and space. Rob

Panda, A quick Pointer in terminology. Basically there are 2 basic types of survey control lumped under the term Benchmark at geocaching. First it is important to know that the word Benchmark in terms of the Geocaching understanding is actually a mongered word. A Benchmark here is any survey marker in the database, but in terms of the actual survey terminology, benchmark is actually 2 words; Bench Mark, and the term is referred to as Vertical control, or in other words, a point of measured elevation. With Vertical control it is important that you know that the horizontal location is scaled, and that location is usually not as accurate as your GPS. This is why with vertical control you will see this "coords off" thing a lot. It is acceptable. These stations were never surveyed in the manner that would make them horizontally accurate. It is ok. The Scaled coordinate is not technically considered wrong, just scaled, and we are allowed to offer an improvement to that if we like. Horizontal Control is often called Triangulation, it could be either optically or GPS observed depending on when it was done. It's horizontal location is to be considered way more accurate than your GPSr will be able to resolve, However you may find that the datasheet will say the Vertical component of that location is scaled. We have no way of testing this to improve it so we don't. On some station marks that were observed wit GPS you will find them to be highly accurate in both the Horizontal and the vertical. There will be no improvement needed for those stations either. It looks like you may have been reading this forum for a while, But feel free to delve back into the many things we have discussed already, there are likely a lot of question that you may have that may already answered, also feel free to ask more any time. Also, feel free to look at the NGS website for their many goodies and most importantly the links that work with the datasheets. Learning to read the datasheet well, will unearth a wealth of knowledge that will be of more help that you might imagine. There is a page there which will define the datasheets many uses to you. In addition, the Datasheet as downloaded from NGS will give fresher data. Data which is a fully 5 years more recent than what is in the Geocaching Database. The best way to think of it is to use the geocaching database to see what the geocachers have found or not found in the way of benchmark hunting, and use NGS for the most recently updated scientific Data, and actual station recoveries. Good Luck! Rob

BDT, Yes there is a difference in origin and orientiation of the 2 coordinate systems. Both Datum use different ellipsoid models. Both Datum use different Geoid Models. One Datum has a grid filled with thousands of survey markers it is trying to accurize as a whole, the other does not. One is trying to be a best fit for North America, the other the Earth. These are reasons that even Least squares wise they are statistically different, but I think that it is likely more miraculous that they are as similar as they seem to be given the empirical differences, not just the statistical ones. The Why of it really does come down to the basic differences as stated above. Over powering the entire set of answers to this discussion is one answer that overrules all of the other answers. The Cause: Before all of this, the Geodesists (in each agency) had to come to agreements as to how the best way to tackle the problems would be. This is the result of the agreement in two different Datum. The Effect: The left hand did not account for the right. Didn't then and still doesn't. Rob

kc2ixe, Sorry, They are meters. In the equations they begin as meters. Every observation we make to justify it used the meter. The factors applied to the equations, equations that use simultaneous adjustments and least squares adjustments, are such that they statistically compare in the Case of the NAD83 the ellipsoid and geoid models as well as the grid of observations, which are the very survey markers you are helping to recover, the math will cause the meter to become averaged if you will, so that everything becomes a best fit. In the case of the WGS84 you have the ellipsoid and geoid models, but they are not the same ones used for NAD83. Also there are physical positions that the WGS compares globally but there are very few as compared to NGS's Database and furthermore their database of physical survey is classified so we cannot know them and use them in comparisons. In any case, the mathematical operations, such as simultaneous equations, and least squares adjustments are applied to the WGS datum as well and as based on the numbers used there it scaled the meter differently than NGS. In terms of the purity of the meter, the meter used, is as thought of in the a-priori state, and was a pure meter to begin with, but the earth ain't flat, and all the equations will have to have some room to move. Scaling factors are in play and I am sorry but it is something we simply have to accept. As a for instance there are other things we have to accept. I like to think I do good work in the field but I can not avoid certain truisms, Nobody can. Like that leveling paths are path dependent and using a different path can skew my results. Like I can take more than one distance reading with EDM between a couple of points and not get the same results, Which is to say more technicallly, Open Traverses rarely ever match. (it is almost safe to say that they never match) Further, my measurement in reality is really a straight line measurement attempting to measure a curved surface. Not exactly a best fit, oh and geodetically incorrect, but we use what we have. Geodetically my measurement is not correct as a stand alone measurement. If I make enough of these measurements and base them triangularly so I can tie points together I can begin to see the curvature of the earth, and when I take them all into a big picture with some applied calculus the "averaging" process will blend the measurements to decide what lengths are the best fit. The new numbers may not concur with my initial observations exactly but they will be close and considered more accurate. This is in essence what happens to the length of the meter. I also want to call attention to the fact that the Meter began as a Geodetic observation. Here was the original formula. 1 meter equals the distance from the north pole to the equator on a path that passed through Paris, France. Then it was divided by ten million. There is your meter. From there they wanted to have an empirical copy and the "Powers that be" changed the length a bit in the process of doing so. You can google all this if you want a better understanding. Today, it is close to what it originally was , but not exactly. Geodesists have folk amongst themselves who are also powers that be as well and they are the people who decide how they are going to describe the earth with a particular Datum. Once they decide, technology marches on and the soon find themselves doing it again. The meter is simply an agreement that happens to be a mathematical construct for measurement. It is the basis for the measurements. It really is. Not much different than a 10K ohm resistor which fits nicely into equations on paper, but can have as much as a 10% variance in reality. In the case of the Meter, after the math is applied, things change. You simply have to accept it, everybody does. Rob

Hi Bill, Sections are actually supposed to be square, and represent a square mile, Sometimes it does not work. The earth is not flat so squares don't fit all the time, and terrain can get in the way of easily surveying a straight line, especially back in the day, So sometimes the line was not straight. Where it changed directions yet was not a section corner was called an angle point. Thanks for asking, Rob

BDT, Google can help you too, In seconds I had this: http://gpsinformation.net/main/ngs-accuracy.html http://gpsinformation.net/main/ngs-accuracy.txt And This Tutorial: http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM Another Tutorial... http://gge.unb.ca/Research/GeodesyGroup/tu...al/tutorial.htm Perhaps you could be more succinct for us. It would seem that the differences between the Datum we have been discussing has really stuck in your craw. We have answered you, I thought Quite well and exhaustively, yet you return with question after question which has been covered already, so what is missing for you? What is it you are trying to achieve or understand? How can we help you? If you don't want help, Ok, what are you driving at? Rob

Trumper. I did say eastern So Cal as a guess. Townships are 6 miles on a side, so are ranges. so I can calc the distance east from the meridian but without access to the data, I cannot see if I was east enough to be in Arizona as based on the location of the meridian, so I guessed East So Cal. It is interesting, But you picture of the station was clear enough to bag it without coordinates, if the Database was up. It wasn't so I couldn't use it, and so I guessed based on recollected deductions and a little detective work on where you are likely to be found playing in your free time. You did fine, You threw down the Gauntlet and I bit. It was good fun. I was close and I am not disappointed. Thanks for the fun, Rob

Kewaneh, No problem! I know that the California Meridians crawl a long way east and it depends on which meridian being used. I don't work that area, and I don't have access to the data, but I do know Trumper caches in California... I also know it is in a state that uses PLSS so... Not having access to the maps at the Moment I could not look and see if the likelihood of this section belonging to a Meridian North or South of where the Nevada state line cuts East forced me to Guess. Now he says it is in none of the States. I am missing some of the thread here real time as I am posting to it at the same time others are. What they may not have realized is that the station has it's solution right on it including the directions of the lines leading to and from AP 5. Angle Point 5 will be the tattletale I imagine and until the database is Up, It is Trumper's Game. I don't have maps for all that at home, but it is a solvable puzzle, Not a mystery. Thanks Kewaneh! Rob

The important point I was making is that the Cadastral Marker informs us of it's location within the system it uses. That is not a Mystery. Well Not to someone in the Survey industry. You have us on the State for now. But I am sure there are only so many meridians who have Townships and ranges at this range with sections that have an angle point 5 and that narrows it down. Bottom line, It does not need to have a Geodetic position in order to be found with the Cadastral system. The Bureau of Land Management has an online database with all this in it and this too is in there. Their database is currently offline for security upgrades and they are not stating when they'll be back up. No Matter. It is findable. Rob

California Has 3 different Meridians, Nevada has no meridian of it's own and uses California's Meridians, Can't recall exactly but Arizona uses them also in part of their state, I can't exactly recall. If the BLM's Site were up, I could sort it out just as I said. Everything is all there. No Mystery, not too difficult to sort out. If it is not in California, that makes sense too as it is Well East of the Meridian it Belongs to. The state lines don't run in straight N-S Lines so the PLSS will cross them at different places. There are only so many places that place can be and it can be narrowed down. Not too hard to sort up with access to the data. We will have Access when BLM is back online. Rob

Pssst, John, Trumper doesn't do benchmarks. Remember? It would appear Thumper doesn't really care that much. Am I the only person reading the entire post here? You guys gotta stop speed reading. You're missing the good stuff! I'll even use an emoticon so you will see I am funning with you here. You might have noticed i was having a little fun with Trumper while I was at it... I just want you all to realize that before this thread take ones of those trollish turns. Eh? Heck, this one too Rob

BDT and all. Relax, I read it fine. I am familiar with this sort of thing. It is something I deal with in return for wages and benefits. I explained where it is. I spelled it out in plain english. This IS the location of the Survey Marker, using the Cadastral method... This Marker does not use Elevation Latitude or Longitude for it's Primary purposes. it is not Geodetic. It is part of the Public Land Survey System. (PLSS) It's primary mission is for use with determining the location of real property. It is located in the State of California, in Township 20 North, Range 25 East, Section 28, and it is angle point 5 on the section border. I would also guess without looking at the map, that by noting the high numbers of Township and Range that it is likely in So Cal, and nearer to the eastern side of So Cal. Grab the right map and you will walk right to it. That is how we find and use them. That IS the Method for finding it. We get in our vehicle and drive to that particular Township, Range and Section. This is Angle point 5. This IS the location. If the BLM website were up I could give you a link to the data along with a Map and a Photo of the area. I could put a little red dot on the angle point for you. You could figure out where to park and hike to it for yourself. Get it? As always, Rob

Highpockets, I did a simple search on geocaching for Stations called Q 197. Countrywide you could say there are a few eh? AF6123 Q 197 FL bench mark disk BJ0972 Q 197 LA bench mark disk BM0289 Q 197 TX bench mark disk DJ0116 Q 197 AL bench mark disk DL0364 Q 197 AR bench mark disk EH0429 Q 197 MS bench mark disk FH0853 Q 197 OK metal rod GB0396 Q 197 KY bench mark disk GB0945 Q 197 TN bench mark disk GM0466 Q 197 NM bench mark disk GX0060 Q 197 WV bench mark disk GX3481 Q 197 RESET WV vertical control disk JF1088 Q 197 KS bench mark disk JV6928 Q 197 MD survey disk KV1928 Q 197 PA bench mark disk 11/19/2004 LC1450 Q 197 IL bench mark disk MD0950 Q 197 IN bench mark disk MU0162 Q 197 NV bench mark disk MW0468 Q 197 CA bench mark disk OE1105 Q 197 NY bench mark disk QB0668 Q 197 OR survey disk RF0501 Q 197 ME bench mark disk RJ0308 Q 197 MI bench mark disk SH0521 Q 197 MN bench mark disk SS1575 Q 197 RESET MT vertical control disk Yes you are getting the picture. Just look back through the bench mark forum, we have already covered a lot and you can pick up on a lot more cool info on these by simply reading up in your spare time. We all have come across some doozies! Good Luck and enjoy, Rob