Sundicator, A Device for Predicting Solar Times and Positions


This square horizontal dial is contained in a clear and black hinged plastic 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 brass ring to a white plastic base with blue felt protecting the underside. The base is marked with a compass circle calibrated from 0 to 180 by 10 X 2 with hash marks at the five-degree points. 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 dates from right to left and from bottom to top to bottom: JAN 7, JAN 30, FEB 18 . . . DEC 7. 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 3,061,137 was granted to George Svboda, Robert K. Jacobsen, and Morris Nozette on 30 October 1962 for an improvement in plastic hinges on cases.


Deborah Smullyan, ed., "Obituaries"., accessed 26 September 2002.

Inventor: Spencer, Thomas

Location: Currently not on view

Subject: MathematicsAstronomy


See more items in: Medicine and Science: Mathematics


Exhibition Location:

Credit Line: Gift of Thomas Dickinson Spencer

Data Source: National Museum of American History

Id Number: MA.333705Catalog Number: 333705Accession Number: 300657

Object Name: computing device

Measurements: overall: .8 cm x 10.2 cm x 10.3 cm; 5/16 in x 4 1/32 in x 4 1/16 in


Record Id: nmah_1215157

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