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The Miriam and Ira D. Wallach Division of Art, Prints and Photographs: Photography Collection, The New York Public Library. "Device developed by specialists of the U.S. Department of Agriculture for eliminating the human equation in determing the end point in cooking jams and preserves. ..." The New York Public Library Digital Collections. 1935 - 1936. https://old-digitalcollections.nypl.org/items/b35e5620-c4dc-013e-7268-0242ac110002
The Miriam and Ira D. Wallach Division of Art, Prints and Photographs: Photography Collection, The New York Public Library. "Device developed by specialists of the U.S. Department of Agriculture for eliminating the human equation in determing the end point in cooking jams and preserves. ..." New York Public Library Digital Collections. Accessed September 21, 2026. https://old-digitalcollections.nypl.org/items/b35e5620-c4dc-013e-7268-0242ac110002
The Miriam and Ira D. Wallach Division of Art, Prints and Photographs: Photography Collection, The New York Public Library. (1935 - 1936). Device developed by specialists of the U.S. Department of Agriculture for eliminating the human equation in determing the end point in cooking jams and preserves. ... Retrieved from https://old-digitalcollections.nypl.org/items/b35e5620-c4dc-013e-7268-0242ac110002
<ref name=NYPL>{{cite web | url=https://old-digitalcollections.nypl.org/items/b35e5620-c4dc-013e-7268-0242ac110002 | title=
(still image)
Device developed by specialists of the U.S. Department of Agriculture for eliminating the human equation in determing the end point in cooking jams and preserves. ..., (1935 - 1936)|author=Digital Collections, The New York Public Library |accessdate=September 21, 2026 |publisher=The New York Public Library, Astor, Lenox, and Tilden Foundations}}</ref>