From the beginnings of X-ray crystallography through the 1950's, data collection was performed, almost exclusively, by photographic methods. These photographic techniques include Rotation, Precession, and Weissenberg photography.
In the 1960's, the introduction of the automated diffractometer made the routine of data collection simpler and more efficient. Below is a schematic of a popular form of the so-called “four circle diffractometer”.

Whereas the various photographic techniques are easily understood as interactions between X-rays and the reciprocal lattice, the four-circle diffractometer is, perhaps, best explained as a “Bragg's Law Machine”. The χ and φ angles serve to orient the Bragg reflecting plane into a vertical orientation (so that the incident and reflected beams are in the horizontal plane). The ω and 2θ angles then establish the incident θ and reflected θ angles, respectively.