Julia J. Peterson's 1983 book, "THE IOWA TESTING PROGRAMS - The First Fifty Years" gives an account of how Dr. Lindquist's tireless efforts to develop and put into practical use the world's first high-speed OMR test-scoring machine during the mid-1950s almost came to naught because of severe signal-drift problems with the 'Lucite rod and vacuum-tube photocell scheme' that was incorporated into the original design. As she quotes Professor Lindquist's colleague, Dr. Rulen, "the intervention of Providence" [Page 114] saved the day! Actually, it was the 'last minute' availability of a new miniature germanium-based solid-state photodiode, the 1N77B, from Sylvania Electric that 'saved the day'. The Archival DVD Folder named as above contains a JPEG-image scan of the 'savior' and my related MS Word File 1955_Spring_1N77B Sylvania Germanium Photo-diode_Mod I_ORG.doc which explains more details. The hard-copy printout of this file is included - on one inch thick caliper stock with a Zip-lock container on the back side containing an actual specimen of the 1N77B. Although the 'providential' availability of the 1N77B saved the MOD-I scanner project, it still had its problems with 'dark current leakage' and temperature sensitivity. It was 'blinded' by the direct light between sheets when not being transmitted through an answer sheet, and thus, a carefully synchronized mechanical shutter was required to block the light between sheets - and always a source of reliability headaches. This problem was solved in the very early 1960s by replacing the germanium-based 1N77B with a Texas Instrument silicon-based 1N2175/LS400 which eliminated the need for a mechanical shutter - a major breakthrough at the time!