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Sundicator, A Device for Predicting Solar Times and Positions

Sundicator, A Device for Predicting Solar Times and Positions

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This square horizontal dial is contained in a clear and black hinged plastic case. There are two narrow pieces of black foam lining the case. The Sundicator is a device for predicting either the location of the sun at a given time or the time the sun will be in a certain location. The instrument consists of a clear plastic circle fastened with a screw to a white plastic base with black felt protecting the underside. The base is marked with a compass circle calibrated from 0 to 180 by 10 X 2 with hash marks for each single degree. The four compass points are lettered. The interior of the compass circle contains a polar dial which is calibrated from 7 P.M. to noon to 5 A.M. by hour with vertical lines at every half-hour point. The horizontal lines of the dial are marked with four columns of numbers: 2, 4, 6, 8; 1, 3, 5, 7, 9; 1, 3, 5, 7, 9; and 2, 4, 6, 8. A table between the inset compass and polar dial explains that each number represents a date range given in the table. There are also columns for "Time Corr[ection]" in the table with values ranging from -14 to +15. The clear plastic circle is marked in red with a scale calibrated from 10 to 80 by 10. The scale indicates the sun's altitude and is to be used as a pointer. There is an inset compass (diameter of 1.6 cm) lettered with eight compass points.
Harold Dodd and Thomas Spencer (d. 1995) received U.S. patent number 2,715,273 for this instrument on 16 August 1955. Spencer was a 1934 Harvard graduate, naval commander, and insurance broker who donated three Sundicators to the museum during a visit in 1969. He sold these devices for some years through Thomas Spencer Enterprises of Santa Barbara, CA. Photographers use sun locators like the Sundicator with a map and parallel ruler to predict when and where the sun will rise.
Patent 2,570,341 was granted to George H. Hake on 9 October 1951 for plastic hinges on cases.
Deborah Smullyan, ed., "Obituaries"., accessed 26 September 2002.
Currently not on view
Object Name
computing device
Spencer, Thomas
overall: 1.8 cm x 12 cm x 12.6 cm; 23/32 in x 4 23/32 in x 4 31/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Thomas Dickinson Spencer
See more items in
Medicine and Science: Mathematics
Data Source
National Museum of American History
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