Wavelength of the WKα1x-ray line

The wavelength of the $K{\alpha }_1$ line from an electron-bombarded natural W anode has been measured in terms of that of an ${\mathrm{I}}_2$-stabilized HeNe laser. This visible laser is a reference point for current Rydberg determinations and for the present-day definition of length. The resulting wavelength value, namely 0.20901 349 Å (0.90 ppm) (energy = 59.319233 keV) appears to resolve historical inconsistencies in the x-ray route to $\gamma$ wavelengths.