An essential item in any proper navigation kit. The Weems and Plath Aluminum Arms Parallel Rule is used to plot direction on a nautical chart. It is comprised of two straight-edges hinged so that they maintain the same angle.
By alternating the moving edge, and securely holding down the non-moving edge, you can move the ruler about the chart while still maintaining the same angle.
Has aluminum arms that join two 18 in. clear acrylic rulers. Weems and Plath lifetime warranty.