A detailed description of the virtual bond method is presented. Simple equations are set up to examine the various relative dispositions of the repeating units along the polymer helix, if the repeat distance and the screw symmetry are known from X-ray data. The method is demonstrated with the examples of β-D-1,4′-xylan helix and the α-helix. Due to the rapidity and simplicity of this procedure, the effect of using different geometries for the residues can be examined readily. Diagrams are presented, from which one can deduce the torsion angles[Formula: see text], ψ for the various values of the valence angle at the bridge atom. This method does not involve a prior knowledge of [Formula: see text] ψ and hence, derivation of atomic coordinates of the residue for Fourier transform or structure factor calculations is simple.