Rulers like this one are used to plot course lines and bearings on nautical charts. They can be rolled across the chart to the compass rose without changing its orientation.

Catalog: NM.3-20
Date: ca. 1900
WL: 50×7 cm (19,5×2.8 in)
Signed: not signed
Origin: unknown
Condition: in good working condition, wear consistent with age and use