A big part of the restoration for NIST’s Million Pounds-Force Deadweight Machine involves calibrating its 50,000-lb disks. The process begins with a standard kilogram mass -- equivalent to a little bit more than 2 pounds. Researchers then "work up" to the 50,000-lb masses through a series of comparisons, using larger and larger masses -- and larger and larger balances. This video demonstrates how the calibration process was done.
Built in 1965, the Million Pounds-Force (equivalent to 4.45 million newtons) Deadweight Machine is the largest in the world. In 2015 and 2016, it was restored for the first time in fifty years, and went back online in June 2016.
Customers who rely on this unique device include US aerospace manufacturers, US military laboratories, and several top-end commercial force calibration labs, which have performed hundreds or thousands of calibrations, all directly traceable to NIST.