Technical Specifications
Key Features and Types
• Mechanism: It consists of two straight rulers connected by two movable metal arms (hinges) of equal length. This mechanism ensures that the rulers remain perfectly parallel to each other, regardless of whether they are opened or closed.
• Captain Field’s Pattern: In versions used in modern maritime navigation, the edge of the ruler features a protractor scale and compass directions. This allows for the direct reading of a course or bearing—using the lines of longitude as a reference—without needing to refer back to the compass rose on the chart.
• Material: Typically constructed from transparent acrylic (to allow the chart to be seen underneath), with arms made of brass or aluminum. Sizes generally range from 30 cm to 60 cm (12 to 24 inches).
• Alternative Model (Roller Rulers): There are also "glider" (roller) models available; instead of hinged arms, these feature a cylindrical roller integrated into a single body, allowing the tool to be moved across a chart to draw parallel lines.
