𝑝𝑟𝑜𝑗 𝑘 -𝑝𝑟𝑜𝑗 𝑘 = 𝑛𝜆 (2) where 𝑎 is any of the 3 lattice vectors. Eqn. 2 is visualized in Fig 1b . If 𝑘 and 𝑘 begin and end on the Ewald sphere and reciprocal lattice points, then both wavevectors projected onto any of the 3 principal axes must differ by an integer number of wavelengths expressed in terms of lattice constant (for more details, see chapter 6 of ref ). As a result, constructive interference is observed.