Parallel rules help draftsmen, surveyors, cartographers, architects, and navigators draw accurate parallel lines. The instrument comes in two main forms: two rectangular straight edges connected by brass or silver hinges, or a single frame surrounding a roller. The first type was known in Europe by 1600, while Englishman A. George Eckhardt is credited with inventing the second in 1771. The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.
The mathematics collections contain about twenty parallel rules and combination instruments, dating from the late 18th century to the late 20th century and ranging in length from 6 to 24 inches. The objects are made from ebony and other woods, brass, German silver, and plastic. They were manufactured in the United States, England, Italy, and Taiwan. They were used for military surveying, in navigation, in business, in art and technical drawing, and for placing handles on caskets. Several of the objects in this group illustrate innovations added to the basic instrument.
The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.