In searching for potential superstructure peaks in the low q z range and the helix maximum at higher q z , first, scans of the small q k space along the q z axis were performed in GID mode under variation of the angle of beam incidence (Fig. 3) . These scans were followed by addressing the far q k space under attenuation of the specular axis, yielding a combination of exposures that provide a partial overlap (data not shown).