The absolute lattice parameters of single- and polycrystalline materia
ls have been measured to within a few parts per million with a high-re
solution diffractometer. The problems associated with 'zero errors' an
d sample centring on the goniometer are eliminated and high precision
is achieved by virtue of the exceedingly high angular resolution of th
e instrument. The high-resolution multiple-crystal multiple-reflection
diffractometer is used to determine the lattice parameter with a sing
le quick measurement on a range of 'perfect' semiconductor-substrate m
aterials, layer structures and inhomogeneous samples. The various corr
ections and alignment procedures associated with this method are discu
ssed.