Of course, because you lose accuracy when you transfer measurements from one tape to another, tape measure manufacturers want their master standards to be as accurate as possible. They use their NIST-calibrated masters to make the tens of millions of tapes that are bought and sold throughout the world every year. That’s because many of the manufacturers of tape measures send their master length standards to NIST for calibration. The accuracy of most of those tapes are still traceable to NIST labs, though. Although NIST calibrates oil gauging tapes and special tapes that are used for events like the Olympics, we don’t calibrate every tape measure that you find in your local hardware store.
Just for some perspective, a human hair is anywhere from 80,000 to 187,000 nanometers in diameter. Using this system, we can measure a meter with an uncertainty of +/-300 nanometers, or 3 parts in 10 7. Many of these distributors send their tapes to NIST to have their accuracy checked against our high accuracy reference laser measuring system, which is among the most accurate tape measuring systems in the world. In this business, inaccurate tape measures can cost the distributor or customer hundreds of thousands of dollars in losses, so being accurate is really important. With so much riding on winning, it’s easy to see why you would want the length of the course to be as accurate as possible. In addition to being featured on the front of a box of breakfast cereal and the pride that comes from performing better than the competition, athletes who win medals and set world records can reap significant benefits, including lucrative endorsement deals.
This is important because the winners of this event are decided based solely on how fast they can complete a course of known length. In 2011, my group calibrated the tape that was used to measure the length of the 2012 Olympic marathon in London. As leader of the Dimensional Metrology Group at NIST, one of my jobs is to ensure the accuracy of tape measures. Anyway, length is still a big part of my life these days, but the units are meters, which is the international unit for length. After getting a degree in business administration and completing my college football career, I enrolled in University of Maryland to study mechanical engineering and went on to get a master’s at The Johns Hopkins University. I went on to play college football at Towson University, but pursuing a rigorous academic degree while playing football was beyond my ability. First downs and touchdowns are determined by precisely marked yard lines and often decided by mere inches, so it was important to me and my teammates that the referees’ measurements were accurate. Many years ago as a high-school football running back, I cared about every yard I could gain my dreams of playing in college, and with any luck the NFL, depended on it. We use them to build houses, to tailor clothes and to ensure fairness in trade and sports, pretty much any situation where we need to know the length of something.
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