SEDIMENT, SPINACH, AND PEE
When you absolutely, positively have to measure something, here's how to make sure your ruler doesn't disappoint.
By Ivan Amato

(FORTUNE Magazine) – TO TAKE THE MEASURE OF your world, you probably use a ruler or two, some measuring spoons and cups, maybe a pen-sized pressure gauge for your car tires, and a bathroom scale to see how well your diet is doing. Other people don't have it so easy: Steelmakers need to know if the right alloy is in a girder; spinach growers have to fill in nutritional labels on their packages; lab technicians have to calibrate blood cholesterol tests. And the specialized rulers they need reside in Gaithersburg, Md., in a decidedly uninviting warehouse on the campus of the National Institute of Standards and Technology.

Inside Building 301, on shelves, in storerooms, and in supercold refrigerators, is America's primary repository of what those in the know call Standard Reference Materials. Without SRMs, it would be nearly impossible to certify the accuracy of millions of measurements. Many measurements eventually would become suspect. The SRMs are like scientific moorings--without something to tie up to, all boats would drift.

Nobody knows Building 301 as intimately as Mark Cronise, a tan, trim 39-year-old who looks as if he ought to be riding a jet ski rather than overseeing some $15 million worth of SRMs. He started at NIST at age 19 and has worked on SRMs ever since. He oversees a staff of six that collaborates with tens of thousands of experts in government, industry, and academe and ships some 15,000 SRM samples a year.

Cronise has a challenge: "You can tell me a number, and I'll tell you the SRM."

Okay. How about SRM 1944? "That would be waterway sediment," Cronise says with a chuckle. In fact, he was among the team of urban adventurers who collected the sediments from six badly polluted sites in New York and New Jersey. "Some were so bad they wrapped us in Hazmat suits," recalls Kurt Fayles, another member of the collection team.

Each bottle of SRM 1944 contains 50 grams of freeze-dried, sterilized sediment in which the amounts of more than 70 pollutants have been measured and certified. Environmental scientists can calibrate their instruments by trying them out on SRM 1944 before testing their own muck samples.

What about SRM 2385? Cronise hesitates, then says, "Spinach!" This SRM is a slurry of blanched, puréed, filtered spinach kept in baby-food jars. It is some of the best-characterized spinach on earth, with precisely measured amounts of calcium, iron, magnesium, phosphorus, potassium, zinc, and antioxidants such as lutein and beta carotene. Food producers use it as a benchmark in their labs; four refrigerated jars of SRM 2385 go for $467.

One more. How about SRM 1511? Cronise explains that it consists of small bottles of freeze-dried urine containing NIST-certified amounts of five drugs of abuse, including morphine and a metabolite of pot. Forensic chemists can use SRM 1511 to safeguard the accuracy of measurements on, say, a defendant's urine sample.

Spinach and urine samples are among the newer classes of SRMs, which for 100 years have reflected the scientific and technological trends of the day. SRMs were first established in response to the growing number of casualties among railroad passengers. More than 4,000 accidents were occurring each year, resulting in almost 13,000 deaths and injuries. The cause was often a broken rail, wheel, or axle. Metallurgists had identified alloys that could take heavy stresses, but for foundries to make sure they were mixing up the right recipes, their labs needed standardized samples for comparison. By 1906, NIST's precursor, the National Bureau of Standards, began selling just such samples, iron chips packed in spice jars.

The SRMs of the next few decades were dominated by metals, ores, and cement--the stuff of city building. In the 1950s and '60s, hundreds of SRMs for the aluminum, titanium, and semiconductor alloys of the aerospace and electronics industries joined the inventory.

The call for new SRMs never ceases. One of the newest is SRM 2921--human cardiac troponin complex, which consists of proteins found only in heart muscle. A sudden increase in the amount of these proteins in a patient's blood can help confirm that chest pains are due to a heart attack, even if the patient's electrocardiogram looks normal. Now labs can use the benchmark--whose protein was extracted from cadavers, dissolved in a solution, and stored at --50° C in bullet-sized plastic vials--to make sure they're getting reliable results, which can help a doctor determine how to treat chest pain.

NIST's most fundamental project these days goes far beyond muck or spinach; its researchers want to modernize one of the world's most venerable standards, the kilogram. It's the ultimate basis for every measurement of every pound of salami and every milligram of ibuprofen. Among the seven basic units in physics (which include the second and the meter) the kilogram is the only one still based on physical objects. A kilogram is defined by any of the 20 cylinders forged out of a platinum- iridium alloy in London in the 1880s and now held in controlled environments at various standards facilities around the world.

The standard meter used to be the distance between two scratches on a carefully tended bar of metal; now it is defined as the distance that light travels in 1/299,792,458th of a second. The standard second is defined as the time it takes a cesium atom to oscillate 9,192,631,770 times between two energy levels. Likewise, voltage and electrical-resistance standards are based on quantum effects that are independent of specific materials or tools.

Then there's the kilogram. Because of sporadic handling, cleanings, and environmental effects--perhaps including the absorption of mercury from polluted air--the masses of the kilogram standards are drifting apart. The drift has been subtle, about a few millionths of a gram in a century. Even so, with those 20 squat cylinders of metal getting slightly heavier or lighter--including the ultimate kilo, known as "Le Grand K" and housed in Sèvres, France--the basis of every weight measurement anywhere has become ever so slightly unhinged.

NIST physicist Richard Steiner is among the scientists around the world who are exploring ways to redefine the kilogram. One "atom-counting" approach is to fashion a silicon sphere with a specific, gargantuan number of atoms whose tiny masses add up to a kilogram. Steiner's group is taking another tack: a kilogram standard based on length, time, voltage, and resistance. The scientists' task has come down to building a superlatively complex balance that compares electrical and mechanical power, sort of the way a normal balance compares the weights of two different piles of stuff. Called a Watt Balance, the system involves wire coils, magnets, subsystems for providing ultrastable electrical currents, lasers, and measuring instruments, including the satellite-based Global Positioning System. Get all that working flawlessly, and you just might be able to do away with the chunks of metal. Steiner and his colleagues usually run the system at night, when vibrations from nearby roads are lightest. He says he and his co-workers tread very lightly around the Watt Balance.

Developing this so-called electronic kilogram might seem an esoteric task for hopelessly obsessive physicists, but Steiner says it's more than that. For one thing, he notes, the definitions of other physical constants, including the mass and charge of the electron, incorporate the kilogram. So if the kilogram changes over time, other constants, which are used in billions of calculations, also will have to be adjusted. And if those constants have to change, the effects can in principle trickle down all the way to your wallet. After all, the electric meter on the side of your house spins its little wheel at a rate that ultimately depends on the charge of the electron, whose value ultimately depends on the mass of a kilogram.