Parallel rulers

Short description: Drafting instrument used to draw parallel lines

Parallel rule in plastic with aluminum arms.

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.

## Contents

* 1 History
* 2 See also
* 3 Notes
* 4 References
* 5 External links

## History

The parallel ruler was invented at about 1584 by Fabrizio Mordente,[citation needed] as well as by Taqi al-Din who died in 1585.[1] However it was not in common use (at least in Europe) until the 18th century.[2]

Captain Field's Improved Parallel Rule

In the 19th century a retired sea captain, Captain William Andrew Field[Note 1] improved the design by adding a protractor-style scale to the upper edge of one rule, and compass points to the opposing edge, which made reading bearings easier.[2] Examples exist of boxwood, ivory or ebony, usually with brass hinges.[2][4] The instrument usually had two links, but longer models sometimes had three,[5] and sometimes the links were scissored.[6] Another variation is the "roller" model which included a cylindrical roller for ease of use.[5]

## See also

* Cras protractor
* Technical drawing tools

## Notes

1. ↑ Captain William Andrew Field (c. 1796–1871).[3] 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 and a medal from the Royal Humane Society.[3]

## References

1. ↑ Fazlıoğlu, İhsan (2014). "Taqī al-Dīn Abū Bakr Muḥammad ibn Zayn al-Dīn Maҁrūf al-Dimashqī al-Ḥanafī" (in en). Biographical Encyclopedia of Astronomers. Springer, New York, NY. pp. 2123–2126. doi:10.1007/978-1-4419-9917-7_1360. ISBN 978-1-4419-9916-0.
2. ↑ 2.0 2.1 2.2 "Captain Field's Improved Parallel… (NAV0602)". Astronomical and navigational instruments. National Maritime Museum. 2009. http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0602.
3. ↑ 3.0 3.1 Rootsweb, Captain Andrew Field
4. ↑ "Parallel rule (NAV0601)". Astronomical and navigational instruments. National Maritime Museum. 2009. http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0601.
5. ↑ 5.0 5.1 "Parallel rules: Rolling and bar types". Mathematical Instruments - A private collection. 2009. http://www.mathsinstruments.me.uk/page39.html.
6. ↑ "Parallel rule (NAV0618)". Astronomical and navigational instruments. National Maritime Museum. 2009. http://www.nmm.ac.uk/collections/explore/object.cfm?ID=NAV0618.

## External links

* How to use parallel rulers

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