Inside a lab near Washington, D.C., there is a stack of stainless steel that weighs a million pounds.

It's part of a unique machine that was built in 1965 and just refurbished for the first time. And in the world of metrology, the science of measurement, this giant is a source of national pride.

"It's famous in its own right because it is the largest such machine in the world," says Rick Seifarth of the National Institute of Standards and Technology in Gaithersburg, Md. The one next biggest in size, in Germany, is only half as powerful, Seifarth notes. "That's one of the main reasons the thing was restored and refurbished."

Why would anyone need a million pounds of stainless steel?

"Fair question," says Seifarth.

Building just about anything, it turns out — from skyscrapers to medical devices to airplanes — requires an understanding of how materials respond to force, he says, and this NIST lab is dedicated to the precise measurement of force.

Force, you may recall from physics class, is just a push or a pull.

"Anybody can think about this: Push your palms together. That's compression force," says Seifarth. Then he links his fingers together and demonstrates trying to pull his hands apart: "That's a tension force."

The NIST's machine uses a million pounds of dead weight — the stainless steel — to generate a million pounds of force.

"You know, we all drive cars," Seifarth says. "Every bit of steel in that car has been measured as to its capability to withstand certain forces."

The control room for the machine looks just like it did when this place was built five decades ago — with old-fashioned green consoles that have knobs and switches. Seifarth fiddles with them, and the red hand of a dial starts to move. The numbers on the dial go up to a million.

"We just put 50,000 pounds of force on it, and now we're approaching 100,000 pounds of force," he says.

The force is being applied in a metal contraption across the room, which is where this machine either smashes or stretches whatever is inside.

Right now, what's in there looks like a squat paint can. It's a device that measures force, and it needs to be calibrated. That's the kind of job this machine does for clients like aerospace companies or the military — or others who need precise measurements of huge forces.

Directly below this control room, in a pit that goes down three stories, are the stainless steel weights.

The weights are disks that look to be about 10 feet across, and they're arranged in a stack. They are linked together, sort of like a chain. So when the machine picks them up, they just hang straight down, in midair.

"Think about a bathroom scale," says Seifarth. "We step on a bathroom scale, and the scale registers because our bodies are generating a force upon that bathroom scale — gravity is pulling us down. The same thing happens with this big machine. It pulls down on something that we are putting in the laboratory upstairs."

Then, when the calibration job is done, the machine carefully lowers its steel weights back down to the floor.

"When they sit back down, you get this low rumble — like a bull elephant," says Seifarth.

Some of these weights had become slightly damaged over the years, and that's why Seifarth and his team recently did repairs. That meant taking the machine apart for the very first time.

The repair job took a year and a half and was nerve-wracking, Seifarth says. He was worried they'd accidentally destroy the thing. Luckily, the people who built it had stashed away extra parts and special wrenches — the tools had been sitting around for half a century.

"These cabinets were filled with stuff. It was like a time capsule," says Seifarth.

The million-pound deadweight machine just restarted earlier this month and is busy working through a backlog of tasks from eager customers.

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