Melvil Dewey may be seen as the father of the library classification system, but he certainly wasn’t the first to conceptualize such a thing; Harvard librarians beat him out by more than 200 years.Today most Harvard libraries use the Library of Congress call number system, but before the adoption of today’s widely used standards, Harvard librarians invented their own. While many users see call numbers only as coordinates to zero in on their item of choice, Houghton reference librarian James Capobianco cracked the codes of the letters, numbers and dots in Harvard’s stacks and shared the results in a recent talk presented as part of the Library’s RTL Shares series.While the topic might seem esoteric to the layperson, the subject presented a unique approach to delve deep into campus history and architecture, and the library community seemed to agree. “I thought, oh man, we are such geeks. This says something about you too,” Cabot reference librarian Reed Lowrie joked to the packed crowd in his introduction. “Yes, we are all geeks.”Early call numbers for the first library at Old Harvard Hall were simple, short and clear: just three numbers separated by periods. The first number indicated the bookcase, the second the shelf number as counted up from the floor, and a third gave the item’s location by numbering volumes on that shelf from the left. Referencing these call numbers, Capobianco was able to conjecture the floor plans of long-gone buildings, giving a glimpse into life at early Harvard.