Solution to the Avogadro constant challenge

The Avogadro constant is a physical constant representing the number of entities comprising 1 mol but was previously been defined as the number of molecules of a substance in a gram molecular weight. The modification to the definition affects the numerical value of the Avogadro constant. The relative atomic mass of the 16O isotope in the 12C-scale is 15.9949, a difference of 0.03% from the old value of 16.0000. Erik Bäcklin, showed that wavelengths measured at incidence angles near grazing were 0.2% higher than the equivalent wavelengths measured by traditional crystal diffraction methods. Manne Siegbahn proposed the local non-SI unit of length for measuring the wavelength of x-rays, when wavelengths could not be measured directly.