Between 1945 and 1949 Shakespeare scholar Charlton Hinman developed the Hinman Collator, a mechanical device for the visual comparison of different copies of the same printed text. By 1978, when the last machine was manufactured, around fifty-nine had been acquired by libraries, academic departments, research institutes, government agencies, and a handful of pharmaceutical companies. Though built for the study of printed texts and used primarily for the creation of critical editions of literary authors, the Hinman Collator was also employed in other projects where the close comparison of apparently identical images is required: from the study of illustrations to the examination of watermarks to the detection of forged banknotes.
"Hinman's invention greatly increased not only the speed at which texts could be compared but also the effectiveness of such comparisons, and it made collation on a large scale possible for the first time. The most famous use of the machine was by its inventor and resulted in his Printing and Proof-reading of the First Folio of Shakespeare (1963) and the Norton facsimile of the First Folio (1968). Hinman estimated that without the aid of his machine, the research for these projects would have taken over forty years. Without the collator, as he himself recognized, his study would have been a "practical impossibility", as would have the work of the many scholars who compiled dozens of bibliographies, produced hundreds of volumes of critical editions, and undertook countless bibliographical and textual investigations on his machine over the next five decades.
"The purpose of the machine for which he was seeking a patent was straightforward and grew directly from the needs of his research. During the Renaissance, the period of his specialty, books were proofread and corrected continually during the printing process, and early uncorrected sheets were commonly bound up with corrected ones from later in the print run. Thus the printed matter in the last book sold could, and usually did, differ substantially from that of the first, as it also could and quite often did from nearly every other copy in the printing. These variations are precisely the details the collator was developed to help detect. The operation of the device Hinman would eventually build was also straightforward. The operator sets up one book turned to a particular page on a platform on one side of the machine and another copy from the same printing turned to the same page on a platform on the other. He or she then views these items, which are superimposed via a set of mirrors, through a pair of binocular optics. After making adjustments to bring the two objects into registration, the operator activates a system of lights that alternately illuminates each page. If the pages are identical, they more or less appear as one; if they are not identical, the points of difference are called to the operator's eye by appearing to dance or wiggle about" (Smith, " 'The Eternal Verities Verified': Charlton Hinman and The Roots of Mechanical Collation," Studies in Bibliography, Vol. 53  includes images of the machines).