Equation 7 · From Origins to Frontier: A History of Scientific Instruments and Metrology
What does this equation mean?
Read the formula alongside the article passage below. Each part has a deeper page with its role in the equation, the supporting passage and nearby citations.
This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text. Read the equation part by part below; each part has a contextual explanation and a link to its mathematical background.
Read it piece by piece
Symbol U
U is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
How to interpret it
Read this expression with the definitions, units, and assumptions supplied by the article.
What the article says around this equation
where m is the test mass, g the local gravitational acceleration (independently and precisely measured at the balance’s location), v the coil’s velocity in the moving phase, and U and I the voltage and current measured electrically. Combined with the quantum electrical measurements of U and I in terms of h , this equation is what let NIST’s NIST-4 Kibble balance measure the Planck constant to within about 13 parts per billion in 2017 — precise enough to underwrite the redefinition that followed [ 5 ] . The BIPM operated its own Kibble balance program in parallel, one of several national and international efforts converging on compatible values of h ahead of the vote [ 5 ] .
Sources cited in the surrounding passage
These citations give research context. Read each source to check which claims it supports.
Return to From Origins to Frontier: A History of Scientific Instruments and Metrology