Station Pointer
date: label: date made
content: 20th century
notes: label: Description
content: To determine where one is going, it is necessary to know where one is currently located. Beginning in the 17th century, navigators combined multiple triangulations to ascertain the position of their ships. With a sextant and a station pointer, sailors in the 19th century could plot locations from three data points as long as they were within view of land.
label: Description
content: Navigators employed a sextant to measure the angles between their position and each of three known landmarks. They then placed the station pointer on their chart and set its arms to the observed angles. The center of the protracting circle on the station pointer would then show the position of the ship. Station pointers were also useful for surveying the geographical features of coastlines, either from the water or on land, in order to create accurate maps.
label: Description
content: This station pointer consists of a brass circular protractor divided by single degrees and marked by tens from 0° to 180° to 0°. Three black-coated anodized brass arms meet in the open center, which has a brass pricker for positioning on the chart. Three brass and blackened anodized brass legs are screwed to the center piece by rings on one end of each arm. Each leg has a thumb screw for tightening in position and an arrow for pointing to the angle measurement. The number 602 is engraved near the top of the center leg.
label: Description
content: The rectangular wooden case has wood built-ins and green fabric lining to support and cushion the instrument. The case is fastened with two brass hooks. It is cracked in the left front corner, and there are several dirt and paint marks. This station pointer was probably mainly used for charting a ship's position, since it lacks the verniers that were typically found on the arms of station pointers employed in surveying.
label: Description
content: Ursula N. Forbes donated the instrument in 1986.
label: Description
content: Compare this station pointer to ID Number MA.333663.
label: Description
content: References: National Maritime Museum, "Charting Instruments—Station Pointer," http://www.nmm.ac.uk/collections/search/listResults.cfm?name=Station%20pointer&category=90488; William John Macquorn Rankine, <I>A Manual of Civil Engineering</I>, 5th ed. (London, 1867), 120–121.
label: Location
content: Currently not on view
topic: label: Subject
content: Mathematics
label: Subject
content: Protractor
label: Subject
content: Navigation
setName: label: See more items in
content: Medicine and Science: Mathematics
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content: Science & Mathematics
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content: Protractors
creditLine: label: Credit Line
content: Gift of Ursula N. Forbes
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1986.0316.07
label: accession number
content: 1986.0316
label: catalog number
content: 1986.0316.07
objectType: label: Object Name
content: protractor
physicalDescription: label: Physical Description
content: felt (overall material)
label: Physical Description
content: hardwood (overall material)
label: Physical Description
content: brass (overall material)
label: Measurements
content: overall: 5.6 cm x 60.7 cm x 18.2 cm; 2 7/32 in x 23 29/32 in x 7 5/32 in