Equation 1 · Part 4 · From Origins to Frontier: A History of Scientific Instruments and Metrology
Symbol U
What this part means
U is an input to the expression that computes the quantity on the left.
Its job in the formula
U is an input to the expression that computes the quantity on the left.
Full expression→Symbol U→Article meaning
The passage around this formula
…simplified form, is: . 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…
Learn the underlying idea
A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.
Open the illustrated variables: a letter stands for a value guide →
See this notation across published equations →
Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.