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Parallel rules


These navigator's parallel rulers are inscribed with full 180 protractor markings. The middle of the bottom edge forms the protractor center when the arms are closed. This tool combines the essential features of a protractor plotter and a basic parallel ruler. Allows courses to be measured from a convenient meridian. Made of extra strong, crystal clear acrylic.
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Click to enlarge12" Brushed Aluminum Arm Ruler140
with Graduations
12 inch length, 0.22 inch thickness, aluminum arms and handles. Wt. 5.5 oz.

#NP140List Price $20.99Only $17.99



Click to enlarge15" Brass Arm Parallel Ruler142
0.14 inch thickness, solid brass arms and handles. Wt. 7 oz.


#NP142List Price $43.99Only $35.99



Click to enlarge24" Commercial Parallel Rules24
with protractor scale. Used to plot a course from a convenient meridian or compass rose on a chart.


#NP024List Price $47.99Only $29.99



Click to enlargeTriple Parallel Rulers136
A new release of an old ship's pilot favorite. This l2" Triple Arm ruler is built to the same exacting high standards as our premium Weems & Plath rulers. The unique 3 rule construction allows greater parallel walk without the diagonal creep associated with traditional designs. Milled with bevelled edges, 0. 1 9 inch thickness, with aluminum arms and handles. Wt. 7 oz.


#NP136$25.99



Click to enlargeBi-Rola Rule Rolling Plotter155
Weems & Plath has patented the Bi-Rola for its vertical and horizontal rolling motion to simplify course plotting calculations, while the unique radial arm allows you to automatically include compass corrections in your plotting. The Bi-Rola is the most completely self-contained device in its class, and will withstand years of use due to its brass and heavy duty plastic construction.


#NP155List Price $87.99Only $72.99



Click to enlargeBi-Rola Rolling Ruler P.R.220
Made with the professional in mind, the P.R. 500 has a considerably larger body than the smaller Bi-Rola rule. Built to take the rigorous use aboard commercial and blue water vessels, the P.R. 500 provides one of the easiest methods invented, to date, of plotting courses. Dimensions: Length 19-5/8", Width 3-5/8", Thickness 1 1/4". Weight: 1 lb. 10 oz. Features: Patented four-way rolling motion, Roller body has protractor markings every 1/2 degree, 1-1/4" magnifying lens for enhancing chart data, Easy to follow instructions. Comes packaged in a protective, durable vinyl pouch.


#NP220List Price $147.99Only $112.99



Click to enlargeParallel Plotter120
The instrument consists of a plotter mounted on a roller. The plotter contains distance scales at 1:20,000,1:40,000 and 1:80,000 to fit the N.O.S. Coast and Harbor Charts and also an inch scale. A semi-circular protractor is included for measuring courses and bearings against a meridian on the chart, and two quarter circle protractors for measuring courses and bearings against a parallel of latitude. Courses and parallel lines are transferred and kept parallel by means of two rollers which are mounted on a slide axis. Used for measuring or laying off courses and distances on a nautical chart. Instructions included. Wt. 5 oz.


#NP120List Price $24.99Only $20.99




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