  We present a method for the precise determination of the full elasticity
tensor from a single crystal diffraction experiment using monochromatic X-rays.
For the two benchmark systems calcite and magnesium oxide we show that the
measurement of thermal diffuse scattering in the proximity of Bragg reflections
provides accurate values of the complete set of elastic constants. This
approach allows for a reliable and model free determination of the elastic
properties and can be performed together with crystal structure investigation
in the same experiment.
