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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 by Fabrizio Mordente, 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 wit ...
points to the opposing edge, which made reading bearings easier. Examples exist of boxwood
''Buxus'' is a genus of about seventy species in the family Buxaceae. Common names include box or boxwood.
The boxes are native to western and southern Europe, southwest, southern and eastern Asia, Africa, Madagascar, northernmost South ...
, ivory
Ivory is a hard, white material from the tusks (traditionally from elephants) and teeth of animals, that consists mainly of dentine, one of the physical structures of teeth and tusks. The chemical structure of the teeth and tusks of mammals i ...
or ebony
Ebony is a dense black/brown hardwood, coming from several species in the genus '' Diospyros'', which also contains the persimmons. Unlike most woods, ebony is dense enough to sink in water. It is finely textured and has a mirror finish when ...
, 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 wit ...
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
Drafting tools may be used for measurement and layout of drawings, or to improve the consistency and speed of creation of standard drawing elements. Tools such as pens and pencils mark the drawing medium. Other tools such as straight edges, assist ...
Notes
References
External links
How to use parallel rulers
Navigational equipment {{navy-stub