The Hinman collator, an early optical collator, was an opto-mechanical device for comparing pairs of documents for differences in the text. Documents that appeared similar were said to “collate”. The collator resulted in rapid advances in the study of literary works.
Invented by Charlton Hinman in the late 1940s, the device used lights and mirrors to superimpose images of the two documents so that differences in text alignment or wording stood out. This resulted in huge improvements in speed and efficiency compared to the traditional cross-referencing of texts by eye.
Hinman used his device to compare the many slightly different impressions of the First Folio of William Shakespeare's works. The printing and bookbinding processes used in the time of Shakespeare often resulted in variations in the pages bound into the final books, and the collator enabled Hinman to describe the exact order in which the Folios had been composited and printed.
In the wake of Hinman's success, the device was purchased by a number of universities, libraries and other institutions (allegedly including the CIA). As more compact types of collator were developed in the 1960s, the last Hinman was built in 1978. In his 2002 survey of mechanical collators, Steven Escar Smith estimates from scattered records that as many as 59 Hinman Collators were produced, 41 of these surviving at the time of his survey's publication. 
The device was developed further by Randall McLeod.
- Smith, Steven Escar. "The Eternal Verities Verified": Charlton Hinman and The Roots of Mechanical Collation. Studies in Bibliography 53, 2000.
- Smith, Steven Escar. "Armadillos of Invention": A Census of Mechanical Collators. Studies in Bibliography 55, 2002: 139.
- Zalewski, Daniel. Through the looking glass. Lingua franca, June 1997.