Fourteen (14) pages, plus appendices with engineering drawings, authored by J. V. McMillin, WLC/MRC Engineering Mgr. The W-400D was an OMR product we developed that could read 30 channels in any of the 80 columns of an IBM tab-card size document, as well as read standard 12-row punched holes in any column. Thus the above key specifications were critical to maintain high accuracy in this combined-mode feature. As an aside, it should be noted - as everyone no doubt knows - that the punched-hole IBM tab-card size document or Hollerith-code format, as it was originally known, is virtually obsolete today as a data-storage medium, but it was Kind of the Hill for several decades until first replaced by magnetic tape in the late 1950's onward, then later by rotating memory (discs), RAM, etc.