A new laser speckle angular measurement (SAM) technique detailed in a paper in Light: Science and Applications demonstrates how slope error measurements can be reduced dramatically. This is important because X-ray mirrors are widely used for synchrotron radiation facilities, X-ray free-electron lasers and astronomical X-ray telescopes. However, short wavelengths and grazing incidence impose strict limits on the permissible slope errors. Although advanced polishing techniques have produced mirrors with slope errors (below 50 nrad root mean square (rms)), many existing metrology techniques struggle to measure them. Additionally, SAM is compact, low-cost and integrates with most existing X-ray mirror metrology instruments.