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July 6th, 2012

Olympic marathon course comes down to NIST calibration

Published on July 6th, 2012 | By: Eileen De Guire

Researchers calibrate measuring tapes of all types in the 60-meter long NIST tape tunnel. Credit: NIST.

Years of preparation go into the Olympics. What we see is the preparation payoff for the athletes, but behind the scenes, there is plenty of pressure to perform at Olympic-caliber levels.

Take the measurement teams, for example. They get one—only one—chance to do their jobs perfectly. No prelims, no semifinals, no finals. Each competition counts absolutely for the measurement guys.

As engineers and scientists, we know that measuring is a subtle art. Measuring tools need calibration, reference standards need to be right, measuring techniques require skill and refinement and uncertainty must be understood and managed.

So, if you were charged with measuring the Olympic marathon course, what would you do? This, in itself, turned out to be a team effort.

The course is 26 miles and 385 yards long. The tool used to measure it is a device called the Jones/Oerth Counter (the Jones are the father-son team that invented it in the 1970s; Paul Oerth added improvements in the 1990s) that is based on counting the revolutions of a geared bicycle wheel, which is calibrated against a tape measure at least 30 meters long. The course is laid out and measured according to rigorous guidelines established by the international athletic governing organizations for marathons and distance races. The rules require that the minimum distance is the official race distance and that the maximum is no more that 40 meters further—that is an accuracy of 1 in 1,000, and only “plus,” not “plus-or-minus.”

The International Association of Athletics Federations turned to David Katz of Finish Line Road Race Technicians, Inc. and his collaborator Hugh Jones to calibrate the Jones/Oerth Counters, and he turned to NIST to calibrate the tape measure used to do it.

A story on the NIST website explains the process. Instead of a 30-meter tape measure, a 100-meter tape measure was used per the specifications of the course measurer. The NIST “tape tunnel” is only 60 meters long, so the calibration using laser interferometry had to be done in sections. Chris Blackburn, the NIST technician whose group did the calibration, says that the job was not very difficult, but his comment in the story reveals the painstaking attention to detail that is involved.

And, by applying the proper tension on the tape to pull it straight and keeping the temperature at 20°C, plus or minus 15 hundredths of a degree, we achieve uncertainties of 0.00018 meters, which meets or exceeds our customers’ requirements in most cases.

Based on the NIST work, Katz and Jones adjusted their calibrations for correct for temperature and errors that NIST found in the tape, which amounted to 13 millimeters over 100 meters. The result is that Katz and Jones found that their measurements of the course length varied by only 1.3 to two meters.

Katz says it best in the story, “I was thrilled with the result. This level of agreement, with a difference of about two centimeters per mile, is pretty remarkable. This measurement was my gold medal.”

NIST has compiled an “Olympic Fast Facts” list that highlights some of the weights and measures relating to Olympic sports, for example, “The heaviest weapon used in fencing is the epee, which weighs 756 grams, or about as much as two empty ceramic coffee mugs.” Very cool.


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