# Parallel rulers

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{{Short description|Drafting instrument used to draw parallel lines}}
{{use dmy dates|date=July 2021|cs1-dates=y}}
[[File:Parallel-rule.jpg|thumb|Parallel rule in plastic with aluminum arms lying on a [cutting mat](/source/cutting_mat)]]
'''Parallel rulers''' are a [drafting](/source/Technical_drawing) instrument used by navigators to draw parallel lines on charts. The tool consists of two [straightedge](/source/straightedge)s 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](/source/Fabrizio_Mordente),{{fact|date=April 2023}} as well as by [Taqi al-Din](/source/Taqi_ad-Din_Muhammad_ibn_Ma'ruf) who died in 1585.<ref name=":02">{{Cite book|title=Biographical Encyclopedia of Astronomers|last=Fazlıoğlu|first=İhsan|date=2014|publisher=Springer, New York, NY|pages=2123–2126|language=en|doi=10.1007/978-1-4419-9917-7_1360|chapter = Taqī al-Dīn Abū Bakr Muḥammad ibn Zayn al-Dīn Maҁrūf al-Dimashqī al-Ḥanafī|isbn = 978-1-4419-9916-0}}</ref>  However it was not in common use (at least in Europe) until the 18th century.<ref name="NMM_2009_1"/>

thumb|right|Captain Field's Improved Parallel Rule
In the 19th century a retired sea captain, Captain William Andrew Field{{refn|Captain William Andrew Field (c. 1796–1871).<ref name="RootsWeb">[http://freepages.rootsweb.com/~heveningham/genealogy/page11.html Rootsweb, Captain Andrew Field]</ref> In February 1833 he rescued 14 sailors from the Sicilian brig Felicita, which was wrecked on rocks at the entrance to Sandy Haven in Milford Haven for which he received the [RNLI Silver Medal](/source/Awards_of_the_Royal_National_Lifeboat_Institution) and a medal from the [Royal Humane Society](/source/Royal_Humane_Society).<ref name="RootsWeb"/>|group=Note}} improved the design by adding a [protractor](/source/protractor)-style scale to the upper edge of one rule, and [compass](/source/compass) points to the opposing edge, which made reading bearings easier.<ref name="NMM_2009_1"/> Examples exist of [boxwood](/source/buxus), [ivory](/source/ivory) or [ebony](/source/ebony), usually with [brass](/source/brass) hinges.<ref name="NMM_2009_1"/><ref name="NMM_2009_2"/> The instrument usually had two links, but longer models sometimes had three,<ref name="Riches_2009"/> and sometimes the links were [scissored](/source/scissors).<ref name="NMM_2009_3"/> Another variation is the "roller" model which included a cylindrical roller for ease of use.<ref name="Riches_2009"/>

==See also==
* [Cras protractor](/source/Cras_protractor)
* [Technical drawing tools](/source/Technical_drawing_tools)

==Notes==
{{reflist|group=Note}}

==References==
<references>

<ref name="NMM_2009_1">{{cite web |title=Captain Field's Improved Parallel… (NAV0602) |date=2009 
|work=Astronomical and navigational instruments |publisher=[National Maritime Museum](/source/National_Maritime_Museum) |url=http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0602 |access-date=2009-06-23 |url-status=dead |archive-url=https://web.archive.org/web/20110802022147/http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0602 |archive-date=2011-08-02}}</ref>
<ref name="Riches_2009">{{cite web |url=http://www.mathsinstruments.me.uk/page39.html |title=Parallel rules: Rolling and bar types |author-first=D. M. |author-last=Riches |date=2009 |orig-date=2001 |work=Mathematical Instruments - A private collection |access-date=2009-06-23 |url-status=live |archive-url=https://web.archive.org/web/20210722202722/http://www.mathsinstruments.me.uk/page39.html |archive-date=2021-07-22}}</ref>
<ref name="NMM_2009_2">{{cite web |title=Parallel rule (NAV0601) |date=2009 |publisher=[National Maritime Museum](/source/National_Maritime_Museum) |work=Astronomical and navigational instruments |url=http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0601 |access-date=2009-06-23 |url-status=dead |archive-url=https://web.archive.org/web/20110609021405/http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0601 |archive-date=2011-06-09}}</ref>
<ref name="NMM_2009_3">{{cite web |title=Parallel rule (NAV0618) |date=2009 |publisher=[National Maritime Museum](/source/National_Maritime_Museum) |work=Astronomical and navigational instruments |url=http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0618 |access-date=2009-06-23 |url-status=dead |archive-url=https://web.archive.org/web/20110609021504/http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0618 |archive-date=2011-06-09}}</ref>

</references>

== External links ==
* [https://boatsafe.com/navigation/rules1.htm How to use parallel rulers]

Category:Navigational equipment

{{navy-stub}}

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Adapted from the Wikipedia article [Parallel rulers](https://en.wikipedia.org/wiki/Parallel_rulers) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Parallel_rulers?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.