A ruling board, a piece of pasteboard with strings tied onto it to make patterns for pressure line rules made by putting the ruling board under the sheet(s) to be written and pressing or rubbing to make an imprint of the lines. This one was used as a cover for Lewis O 171, a loose-leaf devotional manuscript housed at the Free Library of Philadelphia
ICYMI: In the DS Blog, Manuscript Data Curation Fellow Kelly Tuttle explores cross-cultural examples of rules, or layout features guiding scribes while writing on the page, across DS member collections: digital-scriptorium.org/about/blog/2...
Image: Free Library of Philadelphia, Lewis O 171