In 1945, The Bridge on the Drina, by Ivo Andric, was published. In the novel, Andric (who won the Nobel Prize for literature in 1961) tells a centuries-long tale of the Balkans and its tumultuous history — its fate linked to geography, at a crossroads between unsettled empires. For over 400 years, his bridge in Višegrad is a silent constant where children play, lovers meet, and old men smoke and sip wine. When the province of Bosnia and Herzegovina is offered as a kind of spoil of war to Austria-Hungary, Andric winks subversively at the Austrians who come to occupy and who bring their passion for weights and measures: It was in 1900, the close of that happy century and the beginning of the new, which in the feelings and opinions of many was to be even happier, that engineers came to examine the bridge. The people were already accustomed to such things; even the children knew what it meant when these men in leather overcoats, with breast-pockets stuffed with varicoloured pencils, began to prowl about. … No one was able to imagine what they could be doing with the bridge which to every living soul in the town meant a thing as eternal and unalterable as the earth on which they trod or the skies above them. (p. 204) By now, most readers of Photonics Spectra know May 20 was World Metrology Day, a day that celebrates this quiet passion for weights and measures. This year, it was also announced that the kilogram (Le Grande K) would be replaced by an unchanging law of physics. As the meter is linked to the speed of light, so the kilogram would be linked to Planck’s constant. Now, the lingua franca of metrology — the seven units that make up the International System of Units (the meter, kilogram, second, ampere, kelvin, mole, and candela) — would all be based not on physical artifacts but on natural constants. Thanks to those who work behind the scenes to set standards with care and precision, our ability to understand the elements and systems that surround us — both elegant and practical — has expanded: We can calculate the size of subatomic particles or the mass of Saturn’s rings. We can discuss quantum entanglement or examine the surface topography of optics. And we can also rest assured that when we buy a gallon of gasoline, we get a gallon of gasoline. This issue acknowledges metrology with two articles. The first is written by Ophir’s new business development manager, Kevin Kirkham, and discusses methods for measuring high-power fiber lasers. The second discusses discoveries made by a research team from Singapore’s Agency for Science, Technology and Research regarding IRmetrology and visible light. Constants may be a manifestation of emotional or technical needs. That the international scientific community now has a coherent language of constants is a praiseworthy accomplishment. Warmly,