Measure for Measure in 2020

Within the Hartree atomic unit systems, the Schrödinger equation becomes parameter free. But there’s more to it than making a student’s life easier, as Gordon Drake and Eite Tiesinga recount.

In first-century China, emperor Wang Mang standardized weights and measures in his newly established dynasty. Noa Hegesh tells the story of sound as the basis for this standardization.

The assembly of the more than a million single parts of the ITER tokamak requires large-scale three-dimensional precision metrology. John Villanueva Jr gives us insights into the complexity of this project.

Wolfgang Pauli introduced the Bohr magneton as a fundamental unit of magnetic moment during an effort to find a quantum basis for magnetism, as Davide Castelvecchi recounts.

Giacomo Prando summarizes the troubled history of the radian, a unit with the odd property of appearing and disappearing seemingly at will in dimensional formulas.

When you start tearing a piece of aluminium foil apart, you create dislocations in the material. Suhas Eswarappa Prameela and Tim Weihs recount the story of the Burgers vector that is now an indispensable tool for describing dislocations.

As a unit for enzyme activity, the katal is enigmatic but struggles to find widespread acceptance. Soumitra Athavale tells its story.

The tool of choice to measure optical frequencies with extremely high precision is the optical frequency comb. Camille-Sophie Brès explains what makes this technique so powerful.

Watching the ocean’s ebb and flow may be soothing, but the history of the sverdrup unit for ocean flow is more turbulent. Tor Eldevik and Peter Mosby Haugan recount an oceanographic journey reaching high tide with Harald Ulrik Sverdrup and his unit.

Philip Lössl tells of mass spectrometry’s struggles to come to terms with terminology.

The note A tuned to 440 Hz only became the norm for musical performance in 1939 after decades of international and interdisciplinary disputes. Fanny Gribenski retraces this rocky path.

Working in a Mexican restaurant during his teenage years, Mark Buchanan discovered his love for jalapeños. Since then he has climbed higher and higher on the Scoville scale.