The Chain Gang

By The Metric Maven

Bulldog Edition

When I was taking a machine shop class, I was the lone metric advocate. There were in fact rounds of boos when I first brought the subject up. One of the instructors decided to plumb the depths of my ignorance with this question “What units are used to construct roads in the US?” To his surprise I replied “chains, and that makes sense how?”

Originally sections of a chain were used to measure land. Later the length of these chains were decimalized. A chain has a length of 100 feet (US Survey Feet) with each link in the chain equal to one foot. Each foot is then divided into ten parts. This is called an Engineer’s Chain or Ramsden’s Chain. But, most of the country was surveyed with Gunter’s Chain according to what I’ve read. According to Wikipedia:

The chain is divided into 100 links, marked off into groups of 10 by brass rings which simplify intermediate measurement. Each link is 7.92 inches long, with 10 links making slightly less than 6 feet 8 inches. The full length of the chain is 66 feet.

Gunter’s chain reconciled two seemingly incompatible systems: the traditional English land measurements, based on the number 4, and the newly introduced system of decimals based on the number 10. Since an acre measured 10 square chains in Gunter’s system, the entire process of land measurement could be computed in decimalized chains and links, and then converted to acres by dividing the results by 10.

Got that? Well, I don’t, so I decided to call someone who does this for a living. I spoke with a Colorado Surveyor who works on public roads. Modern chains are not made of chain, but are now steel tape measures. When a measurement is under 100 feet, its accuracy is generally best determined with a chain tape. For measurements over 100 feet, Surveyors use an Electronic Distance Meter (EDM). Beyond about 1/2 mile they switch to GPS.

Surveying Chain Tape

The Surveyor indicated that because GPS is a meter based system, the Surveyors measure out all the distances in meters, but then immediately convert them to survey feet. If there is data that is not immediately converted, this is the first step done when it is imported into a Computer Aided Design (CAD) system. The design is then done all in feet.

As we talked, the Surveyor interjected: “I would much rather do everything in metric, and in the 1990s it looked like that would happen.” He explained that the US DOT had mandated the use of metric in the late 1990s. Colorado created and printed up specification books in metric and had them printed—at no small cost. The surveyors began to measure and build in metric. Metric was then met with “resistance” whose origin he could not specify. There were complaints about “machines” all being in inches, and horrible calibration problems. This sounds like the “any excuse we can think of not to change, no matter how ridiculous” method of stopping metrication.  The Feds reversed themselves and said go ahead and go back to the way you were doing it—we’re still not ready for metric. Now well into the second decade of the 21st Century, we are back to using decimal feet to measure our public construction. The same way we did it in the 19th Century.

Then I was surprised by this revelation: The road people have one heck of a time dealing with the bridge designers. This is because, instead of using decimal feet, bridges are designed in feet and inches. One can imagine plenty of room for error and confusion with this situation. Of course if it was all in metric—no such problems.

Architectural firms in the US use feet and inches, yet around the world construction is done in metric. There is no study, of which I’m aware, that investigates how much international construction work may be lost, because other countries don’t want designs bid with imperial units. A UK Metric Views Contributor John Frewen-Lord asserted that there may be a metric reason that US firms are buying up established UK civil and structural engineering consultants:

Although many projects are designed by nominally US companies, most work is done by a local office using local people familiar with SI. In my experience as a quantity surveyor working internationally, the US offices of these companies are woefully unfamiliar with SI. I remember when I was once in Chicago, in SOM’s (Skidmore Owings Merrill) offices, looking over a project to be built in the Middle East. It had obviously been conceptually designed in SOM’s Chicago offices in USC, which they then ‘converted’ into SI – to about 10 decimal places! Ridiculous – not only dimensioning everything to an accuracy of micrometres, but the fact that the resulting sizes and dimensions were wrong for metric products (everything from blocks to light fixtures). SOM’s local office in Riyadh had to re-dimension the building.

Our lack of a coherent measurement system has long ago become an economic ball and chain which impedes US industry and commerce. It is long past time for the United States to reform our weights and measurements, switch to metric, and coordinate their usage across all government agencies and mandate metric for the nation as a whole. We just can’t afford to continue doing otherwise.

One thought on “The Chain Gang

  1. Pingback: Surveyors colorado | Kidoscomputer

Comments are closed.