a pair of straightedges connected by two pivoted crosspieces of equal length so as to be parallel at all times, used for various navigational purposes, especially for transferring the bearing of a plotted course to a compass rose.
Origin of parallel rulers
First recorded in 1695–1705
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for parallel rulers
Historical Examples of parallel rulers
Hence we find him first making brass scales, parallel-rulers and quadrants.James Watt