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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 at about 1584 by Fabrizio Mordente, as well as by Taqi al-Din who died in 1585. However it was not in common use (at least in Europe) until the 18th century.
In the 19th century a retired sea captain, Captain William Andrew Field improved the design by adding a protractor
A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry derives from two Greek words, γωνία (''gōnía'') 'angle' and μέτρον (''métron'') ' me ...
-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 No ...
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 and boxwood.
The boxes are native to western and southern Europe, southwest, southern and eastern Asia, Africa, Madagascar, northernmost So ...
, ivory
Ivory is a hard, white material from the tusks (traditionally from elephants) and Tooth, 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 mamm ...
or ebony
Ebony is a dense black/brown hardwood, coming from several species in the genus '' Diospyros'', which also includes the persimmon tree. A few ''Diospyros'' species, such as macassar and mun ebony, are dense enough to sink in water. Ebony is fin ...
, usually with brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...
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 *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