How to Read a 10' English System Surveyors Linker Rod.
Aug 4, 2009 (Updated May 15, 2011)
Review by DeRango
Rated a Very Helpful Review
Pros:Direct Reading, no calculation or note reduction of Rod Readings.
Cons:Only goes up to 10 feet, which decreases its usability.
The Bottom Line:
A great addition to any surveyor or engineer's arsenal of tools in the field!
Typically a direct surveyor rod is known as a linker rod. What this equates to is being able to hold your levels direct instrument height elevation without the extra calculation of determining your elevation and rod reading for each side shot. Within the realm of surveying there are several types of grading or measuring rods for the purpose of carrying an elevation. Within in surveying is coordinate geometry, which is known as X, Y, and Z where Z is vertical. So for the sake of our review we will be talking about this particular Linker rod and how it works.
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The Agatec 1-16580 is an aluminum rod with a strong coated flexible plastic as the readable portion of the measurements. The handles that tighten and hold the not only the tap in place but the height of the road are constructed of a hard durable plastic with a spring locking mechanism that holds the measurement in place for future reading of side shots. Overall the rod is built to withstand different climate temperatures, field conditions, and everyday construction environment usage. I’ve found that we’ve had the same rod for several years and only require minor lubrication and cleaning of components to maintain the rods integrity and usability.
Before the Agatec 1-16580 aluminum rod we used an older version of a linker rod which was made of hardwood and steel measurement tape. This improved version withstands moisture and changing weather conditions as the plastic does not rust or fade like the metallic rod does. The bright yellow colored tape with large red and black numbers is not only easy to read but gives the reader a direct correlation between odd and even numbers.
Differences between Grading Rods
As a rule of thumb surveyors carry benchmark elevations by using a leveling rod which usually extends to 25 feet. In addition the level rods are usually comprised of fiberglass, and have several sections that will allow the rod to extend higher for varying terrains. The Agatec 1-16580 only has a maximum distance of 10 feet vertically; this can cause a problem if trying to carry elevations along a route that has varying heights or drastic elevation changes. Also the size of the rod makes it more difficult to read at farter distances, however there is no requirement to calculate an instrument height, which saves time and is usually easier/faster to check or mass grade projects and reduces the human error of calculating a rod reading each time you take a side shot.
How a Linker Rod Works
When a surveyor calculates existing elevations or shoots elevation he needs a few components to calculate said grade. You need a known benchmark with type of datum, this benchmark might have been established by a FEMA, GPS, or previous surveys typically referencing sea level or maybe a city datum like Chicago typically runs between 0 and 100. When calculating your height of instrument or HI using a level rod, you take your existing benchmark (let us pretend the elevation of Benchmark Alpha is 100.00) and after you setup and level your instrument you read a 6.34. To obtain your Instrument Height you take the Benchmark and add it to your Rod Reading (100.00 + 6.34 = 106.34) which means your instrument is at 106.34, now ever shot thereafter is recorded as a side shot until you move or “turn” off another point. So if you were trying to obtain the elevation of another point and you read a 3.95 then the existing elevation is obtained by taking your HI (Instrument Height) and subtracting your SS (side shot) (106.34 - 3.95 = 102.39) As you can see this takes time to calculate and write down each reading just to obtain an existing elevation. The linker rod cuts this step out by storing your HI.
When using an Agatec 1-16580 rod it actually stores your HI by setting the rod to the benchmark elevation and all points read after that are the actual elevation in juxtapose to the said benchmark. Confused? Let me explain. If your benchmark elevation is 736.95, you would set the linker rod at 6.95 by telling your partner “up or down” till you read exactly 6.95. Once you get it to 6.95 he would lock the rod at the elevation, and then if you read 3.75 on the next Side Shot (SS) you would be recording a 733.75 as that locations elevation. Basically the rod does the work and thinking of what you and I would calculate when using a standard leveling rod.
Metric & English System
Most of us are understand inches and feet, the English system takes one foot and breaks it into 100 parts using what we refer in the field as 10ths and 100ths. One Inch basically breaks down to .0833333 feet or roughly 8 hundredths if you are looking to convert (3 inches = 0.25’). Metric however is more accurate because the distances are smaller thus on bridge and critical jobs where Millimeters are required they make Metric grading rods which provide a higher degree of accuracy and closure.
Personal Usage and Experience
I’ve used this particular brand of rod for much of my career as a surveyor completing field work and projects of all sizes and types. I prefer to use the Agatec 1-16580 when calculating large sums of mass earth work, curb layout, or underground structural work. I do not like “carrying” a benchmark or running what we call a level loop using a linker rod because you cannot go back and check your math nor can it extend beyond a 10 foot vertical change in elevation. The rod is both easy to read and light weight which makes it very comfortable for the guy running it. If you choose to not maintain the rod then expect it to stick and not work as well as it should. I find reading the numbers and hash marks is a task that is best preformed under 300 feet in distance with a 32x scope maybe 400 feet on a 48x scope, but nothing farther if concerned with accuracy. I also noticed that the rod is not designed for longer distances which is most likely because of the limited 10 vertical change in elevation and why would you want to carry anything with a linker that does not have a mathematical check other than hoping your read is correct.
The Agatec 1-16580 is a great addition to any survey equipment entourage, as it provides a tool to accomplish a great deal of work in a shorter period of time. In addition the rod performs and lasts like a hardworking tool should, also it requires little to no maintenance other than common sense care. Most outfits should equip the engineers or surveyors with this handy tool as a secondary piece of equipment to accomplish certain tasks or a safe alternative to long hand calculations. This particular linker rod is something that would suit anyone looking to accomplish work in the field for collecting data or calculating existing elevations.
Math is a wonderful discovery which seldom lies in the field of engineering and surveying, so remember to close out all of your bench loops by “kicking a leg” and tying back into existing benchmarks or other known elevations.
Always cover your butt by checking your entire notes with a calculator, and even having a team member double check the work helps prevent costly errors.
Don’t leave your traverses or loops open-ended, you must close the elevations of addition and subtraction to determine the error in your readings and if proration is necessary to correct human reading errors.
Auto and Electronic Levels are usually setup on a tripod like the Berger Fiberglass or Dewalt Aluminum.
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