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Parallel rulers are a drafting instrument used by navigators to draw parallel lines on charts. The tool consists of two straight edges joined by two arms which allow them to move closer or further away while always remaining parallel to each other.
In the 19th century a retired sea captain, Captain William Andrew Field improved the design by adding a
How to use parallel rulers
Navigational equipment {{navy-stub
Parallel rulers are a drafting instrument used by navigators to draw parallel lines on charts. The tool consists of two straight edges joined by two arms which allow them to move closer or further away while always remaining parallel to each other.
History
The parallel ruler was invented in about 1584 byFabrizio Mordente
Fabrizio Mordente (Salerno, 1532 – ca 1608) was an Italian mathematician. He is best known for his invention of the " proportional eight-pointed compass" which has two arms with cursors that allow the solution of problems in measuring the circumf ...
, but it was not in common use until the 18th century.
In the 19th century a retired sea captain, Captain William Andrew Field improved the design by adding a protractor
A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles.
Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two sw ...
-style scale to the upper edge of one rule, and compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
points to the opposing edge, which made reading bearings easier. Examples exist of boxwood, ivory or ebony, usually with brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other with ...
hinges. The instrument usually had two links, but longer models sometimes had three, and sometimes the links were scissored. Another variation is the "roller" model which included a cylindrical roller for ease of use.
See also
*Cras protractor
Jean Émile Paul Cras (; 22 May 1879 – 14 September 1932) was a 20th-century French composer and career naval officer. His musical compositions were inspired by his native Brittany, his travels to Africa, and most of all, by his sea v ...
* Technical drawing tools
Notes
References
External links
How to use parallel rulers
Navigational equipment {{navy-stub