Ruling the Edge

Leaving the brass anchor weight holding the chart flat, I reached for a heavy brass parallel rolling ruler lying along the desk's upper ridge. Keeping my faceted red relic tucked safely against my ribs, I positioned my free left palm over the cylindrical roller and guided it downward. The knurled metal wheels gripped the stiff linen parchment with a quiet, dull rumble, gliding cleanly across the inked rhumb lines without veering a single millimeter off course. When it reached the map's southern margin, I held the brass bar steady with my forearm and traced the straight bevel with my index finger. True, parallel tracks cut out any ambiguity.