Rolling parallel rules were used for both drafting and navigational purposes. Six inch bar type rules were frequently included in sets of drawing instruments. Larger ones were used for both purposes. Rolling parallels used for drawing often had edge scales in ivory or, later, celluloid. Captain Fields Improved parallel rules, in both bar and rolling forms were for navigation.
An unusual, boxwood parallel rule by Coombes of Devonport, 15 inches long. The upper portion can be used as a protractor.