News & Comment

Every now and then, an extra second is added to an earthly year — a cause for trouble and debate, as Felicitas Arias has been witnessing.

Nick van Remortel demystifies natural unit systems — and advises what to do when you see a mass expressed in GeV.

The most precise measurements of the atomic masses of the proton and the electron make use of Penning traps, and for the latter, a hydrogen-like ion, as Edmund Myers explains.

The bit is a proper unit of measurement and should be recognized as such, argues Iulia Georgescu.

Michel Van Camp and Olivier de Viron are attracted to the fluctuations in the Earth's gravitational pull.

Some concepts are useful but difficult to quantify, as Philip Ball illustrates with the property of hydrophobicity.

Yuqin Zong sheds light on photometry's fundamental unit.

Enrico Massa and Giovanni Mana expound on the substance of the Avogadro constant.

Vincent Icke paints a portrait of the bewildering cosmological constant.

François Piquemal tells the story of the ampere, which bridges mechanical and electromagnetic units.

Despite intensified efforts, measurements of the gravitational constant continue to fail to converge, as Terry Quinn explains.

Michael de Podesta discusses the current definition of the kelvin — and why it is worth changing one last time.