Before the age of computers, the card index was a fundamental tool for booksellers. A rare survivor, the card index of Leo S. Olschki (1861-1940) contains a wealth of information about manuscripts sold by the firm in the period c. 1900-1945, including those that are now found in Pennsylvania. Cards can shed light on the movements of particular manuscripts, and also provide insights into the workings of the rare book trade. They contain descriptions, which were used to draft sale catalog entries, as well as commercial information, including accession numbers, sale prices, purchase prices in code, notes on provenance, dates, and names of buyers.